Appending ebooks to something is a practice belonging to subcultures on twitter and derived from the meme surrounding the horse_ebooks twitter account. Here are some notes on the cultural meaning of ‘_ebooks’.
  
Various ‘_ebooks’ accounts have been created. What they all have in common is the algorithmic act of sampling source material and turning it into a tweet. On the process behind horse_ebooks:
The algorithm that produces the horse_ebooks stream, like most spammic algorithms, relies on user interaction to grow more effectual. It interprets text as data, and determines which keywords might best promote an outcome like the sale of Cialis or Horse Medical Records. Just as with many of our more popular and less insidious internet applications, the more interaction the algorithm gets, the smarter it becomes. The growing popularity of horse_ebooks has reciprocally allowed it to become better at generating tweets like “The Fear Of lowlife criminals With Environmental Protection” (October 30, 2011; 49 retweets).
While it is true that the algorithm publishes tweets that were, at some point, somehow, written, it is non-author in the sense that it defies the binary border between ebook and reader. It imagines non-authorship in a way that even social media, with its dissolution of anonymity, can enable.
Sure. There is something else going on when _ebooks is appended to non-_ebooks; that is, something that is ostensibly not the algorithmic poetics actioned in the event-space between discourse and code. Something has been extracted from the _ebooks phenomena and has now been folded back into the social practices on social media.
  
What has been extracted? (Or what makes ‘_ebooks’ singular?) It is something that, firstly, plays with the relation between sense and nonsense. horse_ebooks enthusiasts are sometimes criticised for anthropomorphising the algorithm-based expressions. The non-discursive semantic sampling of source material is an algorithmic variation of the creative/aesthetic practice of producing and exploding disjunction. Contra the critics, this does not foreclose the possibility of meaning, only that the discursive dimension of the sample has also been parsed by the algorithm. What is this discursive dimension? The incorporeal materialism of all language. [1. See Foucault’s “Discourse on Language” on ‘incorporeal materialism’: “If discourses are to be treated first as discursive events, what status does this notion of event have? Of course, an event is neither substance, nor accident, nor quality nor process; events are not corporeal. And yet, an event is certainly not immaterial; it takes effect, becomes effect, on the level of materiality. Events consist in relation to, coexistence with, dispersion of, the cross-checking accumulation and the selection of material elements; it occurs as an effect of, and in, material disperion.”]
So a little nugget of sense emerging from non-sense. From the perspective of information theory, this is clearly irrational, because signals do not simply emerge from what is ostensibly noise, noise impinges on signals and so on. The meaning produced by _ebooks twitter accounts is (unintentionally?) meaningful but in a quasi-random manner. ‘Random’ because it is derived from the sampling algorithm, ‘quasi’ because it relies on coded text that otherwise belongs to the logical systems of language. That is, the _ebooks are never quite ‘noise’ because they are, at a minimum, sensible as nonsense.
The _ebooks tweets exist not just as a ‘text’, however. They are better understood as an event. Techniques and technologies of representation (language, media, etc.), like all kinds of communication, are forms of transport. [2. Raymond Williams was very clear about this in his ‘Communication’ entry in the iconic Keywords — where it can mean ‘transmit’ or ‘share’.] Representation brings a time and place into contact with another time and place. The singular quality of this contact is the event of sense. Practices on twitter materially enact this process of representational transport. Retweets are ambiguous, ‘favourites’ are less so.
The practical dimension of ‘retweets’ and ‘favouriting’ modifies the relations of visibility and the relations of valorisation inherent in all acts of communication. The normative content of a tweet does not have to be the content that is valorised; rather, more sophistcated twitter users often retweet in an ironic fashion. Twitter users can choose to participate in these processes of transportation by retweeting, this is obvious; less obvious is the purpose of retweeting ostensibly nonsensical tweets. In the passage of the retweet — the ‘journey’ of the communicational transport — what is gained or lost?
  
For a long time subcultural groups have created entire languages of meaning that appear to be nonsensical to outsiders. This is in part happening here as ‘_ebooks’ is a syntactic morpheme belonging to denotational practices of twitter-based subcultures. Retweeting can be understood as a practice of citation; think of that bloke everyone went to school with who knew every single line from the Simpsons. Citing the Simpsons produced a measure of cultural cache as a performance of cultural taste.
Retweeting does something similar, but with an additional dynamic dimension. The political economy of belonging in online networks not only means ‘following’ the right ‘people’ (or emitters of becoming-sensical content), but also of participating in the passage of meaning as meaning itself is enacted. Not only is the content shared, as per Raymond Williams’ definition of communication, but the becoming-sensical of the content is also shared.
Think of a joke that develops over the course of an evening. The release of tension signalled by the smile (weak) or laughter (strong) is triggered by a disjunction that produces the affective tension present in all humour. [3. “A horse_ebooks walks into a bar.” “The barmen says, “.] Such jokes cascade, but they are also repeated other nights, just as the possibility of such a joke developing is repeated. The algorithmic disjunction of sample text of the original ‘_ebooks’ twitter accounts is pregnant with a similar potentiality.
  
What does ‘_ebooks’ represent?
What happens when ‘_ebooks’ is appended to something?
It is an ironic signifier. Instead of signifying the becoming-sensical of the original algorithmic ‘_ebooks’ twitter acounts, it is signifying the (allegeded) becoming-nonsensical of an actual person’s expression.