If you are assisting, and this includes providing support for someone else's code, or doing "invisible" tasks (setting up a redis cluster or writing end-to-end tests), this often finds its way into one email group or another. In fact I remember the names of the "helpers" as you put it by the virtue of their emails and to that end I value them, just as much if not more, for keeping us shipshape.
IMHO, you should find these emails, and I am sure they exist already, and use it as your metric.
Scott Fitzgerald wrote “Show me a hero and I’ll write you a tragedy.” I say show me email chains, and I will show a hero.
Of course I am not stating the obvious fact - which is that your manager, if he or she is worth their salt, should totally value the role "helping" plays in making good software.