"My friend has a 1950's Maccaferri (also plastic) that is called "The Romancer" and has pictures of spinning records, dancing teenagers, girls in poodle skirts...etc all over it. That thing still plays very well although it was built as an entry level cheap novelty instrument."

I've just added a plastic Maccaferri to my collection and I think it has a wonderfully distinctive tone for playing those Django rhythms.

As for decorations, the only guitar I ever personalised was my EKO ranger6. I was 15 years old, and, with all the imagination of a spotty 15 year old, lacqured my initials to the front.
I rediscovered the same guitar some 25 years later,(still wearing my mark), after a chance meeting with a childhood friend, and negotiated its return home.
C-flat.