I am the lowest of tech smart.
I use Elmer's Washable School Markers and I write numbers across on each block. I then number each row down and write the row numbers on the bottom of each block. Works for me every time. I - I , 2 - 1 , 5 - 1, etc.
Much faster than paper squares I use to pin on the blocks.
The washable markers always wash out. I wash in cold water and cold water Tide.