I have the impression that the lion’s share of all posts on Lemmy are reposts or screenshots from other platforms. I don’t mean links to other sites of course, after all Lemmy is a Reddit clone and thus a link aggregator. I just think that Lemmy can’t survive if there is no way to make people aware that a particular post is OC to a fediverse-Plattform. I suspect that the Lemmy community would appreciate the effort that went into creating OC that wasn’t posted anywhere else - there’s just no way to tag Lemmy OC.
Yes, sure. But none of the major communies have that hint in their description. Meaning this practice is not common in most of the major communities. For example: I have not seen [OC] on any post in /memes.
Edit: It’s common in /pics. But that is a given.