The only notes I am familiar with that had the yellow seal were the "Operation Torch" WWII issues and gold certificates. Other than those, I do not even take a second look at these notes. Glad to see that there is a forum for this since I also have seen some on the bay.
I just saw a yellow seal and serial number 1963 $5 bill while on eBay last night. The seller states that's it is rare, but I'm guessing that it isn't since I've read here that the only yellow seal $5 notes are from 1934 - is this correct? Any advice would be appreciated. Here's the link to the auction: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230514069281&ssPageName=STRK:MEWAX:IT Thanks!
Same as the $2's discussed higher up the thread: Anything with the red seal/serials can be bleached to orange or yellow fairly easily. The 1963 and 1953 $2's and $5's are the most frequent targets, but every now and then you see a 1928 $2 or $5. I even saw one low-grade 1928 $1 that'd gotten this treatment! Still waiting to run across a yellow-seal 1966 $100....
Here's another one of these manufactured "rarities" this time it is a yellow seal 1928 $5 note. http://www.ebay.com/itm/1928-C-5-Fi...553?pt=LH_DefaultDomain_0&hash=item2a1d83c5d1