"Block letters" refers to writing or printing letters in a straightforward, simple, and clear manner, where each letter is individually formed and easily readable. Full definition
We still print — i.e. write in block letters — but I wonder how long even that basic ability will last. (slaw.ca)
Each painting in the exhibition followed an identical format: a phrase quickly written out in black block letters on a primed canvas. (thesilo.raphaelrubinstein.com)
Hanging big block letters on any wall in your home can create a beautiful atmosphere that leaves a great impression with guests. (pbteen.com)