If you want to make a 'stealth' button..my approach when external switches are not an option.. get a reed switch (used for alarm systems for windows),
There's normally open/normally closed variations.. place it somewhere like just under the lower corner of the monitor bezel (depending on your cabinet's design)
and glue a (small!) magnet to a quarter/token.. just big enough to activate it, not enough to interfere with the CRT.. one of those magnetic ad cards might do..
(Or avoid crt interference altogether and put it anywhere you want. behind the marquee?)
then just move it into position when you want to activate said secret switch. Lose the special quarter? make another. Work on your sleight-of-hand, and you could mess with
your friends who try activating the switch with their quarter.. hehe.