Re: Seriously though...
S'what I used to do, a hand drawn arrow, with spidery "click here" messages. In the early days printed on to a sheet of paper and given to the colleague(s) in need of help. That sort of thing. A few years later getting my hands on a decent free programme ( when personal computing was still not so common) that allowed me to annotate screen shots was a God-send. Can't remember what it was even called now, decades later.