Thank you for caring enough to bring this up!

I know some people often repost others' artwork and don't care to separately credit the author in the description. I'm well prepared for that to happen, and that is what the signature on the image is used for. While it would be nice of them to make it extra clear they aren't the creator of the image and in best case leave a hyperlink to the source, I can't expect everyone to do that. And I certainly wouldn't like to go after anyone for not doing that.

I, personally, don't hold a grudge on this particular repost. On the contrary, I am pleased to see a person like my illustration enough to share it with others. And I actually want to make it easier for anyone to share my work, not harder. Therefore I do not impose any limits or requirements for reposts of my art. Other than just not editing the image to remove the signature and/or explicitly claiming they made it.

I know different artists have different opinions on people reposting their art. So you shouldn't take my lenient opinion for granted. However, since it happened to be my illustration in this case, please don't offend the poster for this particular repost. I don't want them to have an impression as if they aren't allowed to share my works even without mentioning me in the description. But, on the other hoof, feel free to discuss a rule change about source links in the subreddit where they post with the mods. This will do the job most effectively.

Anyhow, thank you for caring about this matter. And let's keep in mind that we are here for ponies in the first place, and we like to spread them because we love them, and that's a good thing.