This comes from the old phone patch protocol:  “star-up, pound-down”

But, with Allstar, you can configure this to be whatever you want in rpt.conf

cop, 6  is the function to key up the transmit or you can use the keyword “autopatchup”

for dropping the PTT you can configure a function for “autopatchdn”.  On some distros this is function *0

But the “#” down is probably  built-in and goes way back …

Ken