As you can see from this page, there are original sample SMOM plates around, even if this does not mean they are official. Since the letter is totally written in Italian, here's a translation for you, but please forgive my terrible English: to translate is much more difficult than to write directly!
"As answer to your letter, written on February the 28th, 1974, I'm pleased to tell you that I made a back car aluminum plate, with the SMOM print and three following zeros, be sent to you.
The cost is 11.200 Liras plus shipment costs, but I don't know these yet and I'll tell you after it will be sent.
In the hope to have make you satisfied, my best greetings."
11.200 Italian Liras in 1972 were approximately as much as 45 Euro today and means about 45 US dollars.
I did blur and defocused the addressee of the sample (who doesn't own it anymore anyway) and the signature with the name of the sender, as I was asked to do it.