T is for...

 It's the letter T for Sunday Stamps

Part of Canada's far and wide set, issued in 2025 this stamp features the Thousand Islands (and the stamp is Tiny)

Here's a Train stamp from Belgium, issued in 1985 as part of a set celebrating 150 years of rail transport. Link to the full set

And stamps celebrating Three Spanish Theatre festivals from Eva, who wrote that she has visited Two of the theatres.

Explore the links to more T stamps over at See it on a Postcard