Looking for neon signs or tavern/restaurant signs using the traffic
sign of "Yield" with the red and white colors.  Also looking for any
business that trademarked the name "Yield."

There are four current federal US trademark registrations for the word "Yield":

#2815026, for "periodical publications, namely, magazines and magazine
inserts in the field of agriculture."
#1700110, for "cleaner, degreaser, and rust remover for metal articles." 
#1308591, for "non-adherent medical dressings." 
#1351853, for "jeans." 

This is distinct from those many businesses that may be employing the
word "Yield" as a trademark but who have not sought federal
registration.  These are called "common law trademarks," and there may
be hundreds of those.  For example, if some guy in Des Moines hung up
a triangular red and white sign with the word "Yield" on it in front
of his bar, that's a common-law trademark, and the guy has rights in
that word and design as a mark for tavern services as of the date he
first hung out the sign--even if he never files a federal registration
application.  Are you after all these common-law marks as well?