Welcome to oldgas.
Don't be discouraged, many of us have at one time or another unknowingly bought a reproduction sign. I have one in my collection that I keep as a reminder to do my home work before I buy. 90% of all 11 3/4" are repro's. Ask questions on this site, buy collector books, go to gas and oil shows, and talk to other collectors. Education is the key.
Sent from a lumpy rock in my lawn using Hammer & Chisel