I just keep track of the hives and not the boxes since boxes can be utilized on a few hives during the season.
I only use numbers and put them on the outer cover. I use 2 inch sticky numbers from Home Depot. If a hive is combined with another, the hive that has the queen will be the hive number.
In my inspections, I simply look for eggs, queen or swarm/supercedure cells and note the date. I also track when I add a box to a hive.
My "Bee Diary" is done in Word and is restarted at the start of each season.
I print out the entire diary and put it on a clip board. I hand write notes on the clipboard when in the field and then transcribe them after a few inspections. Once the updates are done, I reprint and replace the diary on the clipboard. This gives me the hive's history for the year and refer to it often when i inspect a hive.
There are apps for smart phones but it is too hard to handle when doing inspections. It is much faster to write shorthand notes and transcribe them later.
I am managing about 40 hives right now and this seems to work for me.