the most i have ever come to showing respect is actually taunting at the beginning of the match, there is no action that would turn such an action into a negative, unless my opponent is being really sensitive and thinks "wow he must be very cocky to taunt before we even start fighting!" which is never the case, recently though i fought a japanese player...or so i assume because of the ID name and he used Ness (witch btw is my most hated Match Up) so i was already going into the fight all negative and preparing my salt to flow, but at the beginning he crouched, and Ness crouch sorta looks like a bow alongside the villagers, so i was using Mac at the time and did the same, though his crouch looks like hes about to curl up into a fetal position and cry hehe,
but this is actually off topic as you ment to show a respect at the end of a match since its usually this time people just drop out quickly before the next match, so im with you, to just crouch and stay like that unless your crouching animation looks like a bow so just do a quick tap, and others is to just not do anything...which can feel lame, so usually i just run and jump off-screen or do a special move and hope they rematch me so i can do what i posted above, hoping they get the message of "Good Game"