Just clean it off afterwards, they don't have chips in them like today's smart cables, just clean them off and dry them off and they'll work just fine afterwards.
The I²C bus on pins 12 and 15 is definitely a serial interface, and arguably each color is serial, even if they're not... the traditional sort.
It is quite amusing how many less ambiguous serial connectors they could have trivially chosen. PCI-E, ethernet (8P8C), SATA, SAS, HDMI, FireWire... the options are numerous.
They look similar but a VGA port has 15 pins and a serial port has only 9. Serial ports like this one were really common before USB was used. You would plug peripherals into it kind of the same way you use a USB port. Mice were probably the most common use, but you could plug a lot of different things into them.
Of course it is like USB since the S in USB stand for serial; Universal Serial Bus.
I don’t remember if RS232 was plug and play or hot swap though. I think you might have had to boot with those plugged in. PS/2 I think you could? And of course USB you can. Good times.