Here is the one that sold a Mecum. The colors are OFF on the one you have. Take a look at the "I" in OILS. Top of the I is sloppy. The whole bit looks sloppy as well as the fired porcelain is not consistant. I don't have it my hand, but I doubt very seriously that you have an original sign.

https://www.mecum.com/lots/RA1016-264852/gold-medal-oils-sign-dsp-30-inches/