A further check into the "trademark" reveals that the "HOTELetter" (along with "Writeaways" and "Express It Notes") was marketed by Douglas B. Guy Advertising and Marketing of Palo Alto, CA. Douglas B. Guy (1919-2007) was the President of the Company which was started in 1961 and dissolved in 1990.
Here's the US Patent Office Trademark information:

It seems as though it was a short-lived product that never quite caught on, although you can find some on
ebay, BidStart and
Amazon (most postally unused) with advertising from major hotel chains like Best Western, Sheraton, etc., from as far away as Hawaii and England, and all around the USA.