Arcade buttons using a serial interface
USB ports are a digital interface and an arcade button is an analog device so how do those two work together? The serial port. Once common on computer the serial port can be added inexpensively by an adaptor. Just do a web search for "serial to USB adapter" and you will find many inexpensive options.
Using a serial port you can have up to 4 buttons each with different commands. A serial port has 9 pins and by connecting arcade buttons to different pins you can trigger different commands. Pin 4 is the common pin and pins 1, 8, 6 and 9 can each be associated with a different command using the same pull down style menu in the serial port setup (see wiring example 1 below). The squares labeled CD, CTS, DSR and RING will each light up green when they detect a button press for testing proper operation (see example 2 below).