It should be questions like:

If a school bus is stopped, with it's flashing lights on, what do you do?
At a 4 way stop, who proceeds first?
How close should you pass by a bicycle.
Can you park in a bicycle lane?
If an emergency services vehicle comes up from behind, what should you do?
If an emergency services vehicle is stopped on the side of the road, how should you proceed?
If a traffic light is not functioning, how do you proceed?

The actual answers depend on local laws, but if you don't get ALL of these right, you should not be driving.

One explanation, at least here is Vancouver, is that Mercedes, BMW's, Porsches, etc. are very expensive, and many buyers seek to save money by eschewing electronic turn signals, driving lessons, and other such extras.

I think that aiming your left hand down would signal "I'm stopping", which could be problematic if the motorist decides to go around you and turn right. After all, you indicated a stop. Perhaps signal a left turn and go straight? It might tick them off but I'll bet the WTF is he doing will make them hesitate to hook you.

For what it's worth, some cyclists just point where they're going and they say it works. The only downside (this is second hand) is when you point left to signal and the motorist thinks you're telling him to go around you on the left. It might work pointing forwards though, at just enough angle for the car behind to see it. (?)

I think most cyclists who have this problem, have the problem, because they are riding as close as they can to the right curb. If you ride out further, say a meter (a yard) from the curb, then you automatically indicate your going straight, by staying further out. If there is a right turnout lane, stay out of it, cars that are turning right, will then go behind you and make their turn to your right. You must remember to stay predicable, if you act like a proper vehicle, then other cyclists and drivers will treat you as one.

Left hand pointing with index finger is not the same, I think as a stopping signal which would be indicated with an open palm. Anyway, that's what I do and I do it not exactly hugging the right shoulder but slightly in the through lane. Only an idiot or someone who just does not care could mistake my intention. Anyway, it has worked for me where I ride. Can't say what might be the case elsewhere.

If you can go around the obstruction without leaving your lane, then it's no problem. Just like a car, if you want to change lanes, you first have to yield to the cars that are already there. And if there's no opening, you wait.

I don't think I've ever seen a marked bike lane that's only 1-2 feet wide.

In this case I turn my head and try to make eye contact with cars coming from behind, then do a "left turn" hand signal and proceed per your red arrow. If it is apparent I am going to get creamed for doing it, I "go blue" and cross ped style. This last is very rare.

In regard to the "bike lanes" I am simply referring to the shoulder to the right of "the fog line" (correct terminology?). The white line indicating the right limit of the lane. There are only a few places in town where an actual bike lane is indicated. In regard to the obstruction, at 15, 20, 25 (downhill) mph. there is often not time to discern an obstruction such as a twig or stone in the mottled shadow of tress until the last minute. Seeing it, slowing down and "waiting for the cars that are already there" does not seem like a practical answer to me. But this is getting away from my original post which was about intersections (in my area) and principally ones without traffic lights).

I find this situation particularly problematic on highway overpasses where traffic in my lane will be exiting right to get onto a highway. I am inclined as well to use a hand signal but it is important to know what you are dealing with with a mirror or a glance back.

M1 Abrams Battle Tank. maybe one with a water cannon on top..

The problem is, when you start making up your own rules, nobody else knows what you've made up. If I were in a car, seeing a cyclist pointing to the road would NOT tell me they were going straight. Maybe they want me to put my bumper *right there.* I hope you understand the necessity of yielding to existing traffic before changing lanes - no matter what obstacles are in front of you. Popping out in front of a semi could have adverse consequences, no matter how much glass is on the shoulder.

Is it a case of making up one's own rules or simply signaling intentions? When a cyclist comes up to an intersection where a motorist, waiting at a stop sign, waves him on, is that not helpful?

Also, the three feet rule for motorists passing cyclists helps avoid the sometimes erratic path of a cyclist going up a hill or avoiding a minor obstruction not visible till the last minute.