Here's a set letter bricks which are compatible with Lego blocks.
All of these can be printed without supports.
I recommend printing them directly onto a smooth print bed like glass, without using a raft (In my test prints, the letter “A” was printed with a raft, while the “B” was printed directly on a glass bed and it has a much better fit).
My setting in Cura was "Initial Layer Horizontal Expansion = -0.1mm
Included is a full set of upper & lower case alphabetic characters, plus digits and a fairly large set of symbols.
The author marked this model as their own original creation.