OK Used Cars,
I took a few pictures of my Keyholes (one is a 46' and the keyhole blank is a 40').
You have already mentioned some of the reasons why I too felt that this sign could be reproduction. A couple more issues about that sign that concerned me are:
How irregular the Texaco letter are (the TCO are longer than the EXA).
The Veribrite stamp has been used on Texaco reproductions before (there have been a few double banjo, white T, no smoking signs with that stamp on it). Very FEW Texaco signs after WWII had an ink stamp on them (I haven't seen any, but I'm leaving open the possibility). Of course with the exception of the Canadian made P&M signs.
After WWII Texaco switch to a three digit sign code (##-#-##) , this is stamped with a two.
I'm not trying to beat up your sign, and I could be wrong (I'm just like everyone else on this forum, a student of collecting). In my opinion, these are the type of signs that will destroy our hobby!
I too believe there was about a ten year phase out, but in my opinion Texaco was quick to change their signs (they were slower to change their can designs, especially their Marine cans, and handy oilers).