I've swapped comic trades before (individual issues of comics gathered together into longer books) but I can't seem to discover if the individual, single issue comics are allowed to be swapped. Best as I can tell, I can't see any ISBN number on the individual comics and I don't see many of them on PBS. So are these allowed or not?

Good question.  No they can't be posted here.  Bound collections of comic books are fine.  Single issue comic books often contain advertising and can't be send at the media mail rate, and in any case aren't postable here.  If you put the term "comic book" in the help center search, you'll find the explanations of what can or can't be posted.

What Patty said.  Comics are not eligible for Media Mail and are not postable FIFO per PBS guidelines.

From the Help Center:

Not allowed:

• Anything that is not a book (this includes calendars, coloring books, blank journals)
• Anything that contains advertising (such as single-issue comic books or comic book digests or magazines)
• Advance Reader Copies* (also known as ARC s, Review Copies or Uncorrected Proofs--these are not the final versions of books)
• CD-ROM books/e-books (books that must be read on a computer)
• Burned copies of audio books
• Xerox or otherwise unoriginal copies of books
• ...

Thanks for the info!