Dating the age of your DP-2 prism
The DP-2 was Nikon's first prism using Light Emitted Diodes (LEDs). However, the electronics were not perfect, and Nikon had to make seven design changes to eliminate LED failures. Each varient is depicted with a colour dot under the shutter speed knob coupler.
DP-2 shutter speed knob coupler, with a red dot DP-2 colour dots, dates and serial numbers