Hi gearhead,
We really need to see good photos of the thermometer to give you any help.

The key element is the tow truck graphic. How old does the truck look? Is the graphic large and detailed?

If it is porcelain it would be worth more than a painted sign. A painted sign with surface rust just depends on how bad the rust is.

The phone number with 2 letters and 4 numbers does say it is somewhat old. Urban areas after World War II standardized 2 letter, 5 digit phone numbers. In the mid-1960s new phone numbers were issued with all numbers and no letters. So your phone numbers could be rural or pre-WWII. Not much help for figuring the date of the sign.

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Jim "Oldgas" Potts
Your host and moderator

Jim "Oldgas" Potts
Your host and moderator