Is there an English word (noun or verb) for a quick and short reminder? Imagine a friend reminding you five times a day to take your medicine. He doesn't actually tell you, but rather gives a clue, so that you will remember it on your own. The closest word I can think of is poke, but there are probably more possibilities. Maybe there are short and well-known synonyms.
If your friend walks into the room, and gets your attention by pointing to his watch, he has signaled that it is time for something specific. Perhaps the word "cue" would also apply. Pointing to his watch is a visual cue.
Your friend could also supply a verbal cue, by saying, "Do you remember what time it is?"
Prod might also work. "My friend prods me to take my medicine every day after lunch by silently placing a glass of water on my desk."