Interesting "Number 1 Team" license plate...

[Mr70]

Those are from the Chevy truck body plant at Indianapolis.
I'm pretty sure that it was done by that actual plant,since it's silk screened not embossed,and could be done inexpensively and not a major production.
I have seen them before and referenced in literature,from other plants etc..
Different plants had carte blanche to advertise if they wanted,and Indy wanted.
I consider these a Vintage novelty item,if that makes sense.Not taking anything away from them.They promoted items like these throughout the 1960's 70's & well into the 80's.
Even some of the Sales Dealerships did this as well.