The National Intelligence Service didn't come into being until 1999, within the 20 year rule, but I'll give you a brief rundown since I know what this is.

That said, the inscription on the back reads:

국어정보원장 - National Intelligence Service Director 음이온방사기능 - Anion Radiation - this is referring to the glow-in-the-dark feature, I imagine.

Here is an image of a similar watch with a different bottom inscription. This one reads:

원적외선방사기능 - infrared radiation function - again, the glowing function.

Here is a blog (in Korean, sorry) with a photo of the front of the watch, the same as the one you've got.

Sorry to say, but your watch did not belong to the Director General of the NIS. In Korea, there are a whole slew of emergency numbers: 119 is for fire and ambulance, 112 is for the police, 117 is for reporting school violence, etc. But, 111 is the number to report spies to the National Intelligence Service. If you call 111 and report a spy and it's a good tip, you will receive a watch from the NIS. It's not particularly valuable - it's just a quartz watch - but it's something you can wear around and show of your patriotism.