Driving at the posted Speed Limit

I do a lot of driving. It is amazing to observe other drivers and their foibles. I've previously mentioned my pet peeve of not using turn signals (Clue Signals?). But I have recently noticed something about Speed Limits.

There are not enough signs indicating what the speed limit is in various locations. After turning onto a different route, there is no indication how fast a driver can go in that particular area. Now I know (according to the booklet handed out by the DMV/Secretary of State) what the expected/allowed limit is in unposted areas, but in urban locations, it might be different.

Also, as confusion arises as to the appropriate limit, some drivers tend to go slow - which may be OK until a limit sign is visible.

What ticks me off are the drivers who go too slow ( when it is obvious other vehicles are passing them by), or those who feel the limit is a 'suggestion' and decide it doesn't pertain to them and 'whiz' by me like they were shot from a cannon (Detroit drivers being a primary example). And the 'speedy' drivers honk, blink their lights, tailgate, and issue a hand gesture as they go by.

Well, I am issuing to them their own official "Single Digit Salute" and wish them well (hoping radar is operating just down the road).