I ran the sound board for almost every play the last half of high school, and while I’m sure I didn’t have nearly as many cues as a stage manager, I had quite a few.

I always used erasable markers (I got the ones linked as a gift one year which is why I used them, though there are many other brands that come in smaller assortments and are cheaper) that way I could color code mic cues vs music cues vs sound effects vs etc.

I used the flags you pictured to mark scene/acts, but I used markers to code everything else. It was also super easy to make a key so if there was an emergency (I also did costumes and had to run backstage to fix a malfunction more than once) my assistant could follow the cues easily.

Edit: whoops markers not highlighters