I'm pretty sure the first two #'s under a thumbnail are likes and upvotes, but can't find a description of the other letters and numbers (eg. C0 Q C). They seem to be randomly applied as two very similar posts will have vastly different 'tags'...
Topic: Thumbnail tags?
Posted under Tag/Wiki Projects and Questions
The C followed by a number is how many comments are on the post.
S, Q, or E mean safe, questionable, or explicit.
The last segment is for things like "has parent" (P) "has child" (C) "pending approval" (U) [ie "unapproved"]