I wish I could have found the original opening credits scene....but I'll settle with the title card...and the theme, of course, which is probably one of the most famous in Japanese television history. It's been used in a lot of other TV shows for effect; in fact, the first time I heard it was on a parody skit done on the Drifters' comedy-variety hour, "Hachi-ji Da Yo! Zen'in Shuugo!"（８時だよ！全員集合！...It's 8 O'Clock! Everybody Get Together!)where the comedians were doing their own version of the cop show....without pants. But I can say that I have also actually seen a few episodes of the series itself.
On English Wikipedia, the theme song was described as being "mariachi-like..." Not quite sure if I agree with that description; I think the song is more a funk-rock ode to life in the big city. You just get that urge to smoke a cigarette when you hear it. In any case, the song was composed by Katsuo Ono（大野克夫）, a former member of the Group Sounds band, The Spiders (whose work is already profiled), and it was performed by the Takayuki Inoue Band（井上堯之バンド）, composed of members from The Spiders and early 70s supergroup PYG, in itself composed of the remaining members from the other Group Sounds bands, including The Spiders and The Tigers.
The above is a commercial parody of the original series for BOSS Iced Coffee, but if you look carefully, you may recognize a fellow who's just been nominated for a Best Supporting Oscar. I think he should get the Oscar right now for just performing in a Japanese commercial.