Knock or ring the bell?

Either, once. The problem is repetition rather than the method. Repeated knocking or ringing reads as pressure and is the most common complaint homeowners make.

How long should I wait before leaving?

Long enough for somebody to cross a house, which is longer than it feels when you are standing there. Then log it as not home and move on.

Is ignoring a no-soliciting sign illegal?

In some jurisdictions, yes, and in others it is grounds for a complaint that costs the company more than the door was ever worth. Treat it as binding either way.

Door-knocking etiquette

Good door etiquette is mostly about reducing how threatening and how long the interaction feels. Knock rather than lean on the bell, stand back from the door, do not block the doorway, and leave the moment someone asks you to. Some of this is manners and some of it is law: no-soliciting signage and do-not-knock registries are legally enforceable in a number of jurisdictions.

Manners, and what they are actually doing

Every convention here reduces either perceived threat or perceived duration. Standing back from the door, knocking once rather than repeatedly, not filling the doorway when it opens. None of it is politeness for its own sake, and all of it changes how the first seconds land.

Repeated knocking in particular reads as pressure. If nobody has come after a reasonable pause, the outcome is not-home and the door has told you what it has to tell you.

The parts that are law, not manners

No-soliciting signage, municipal do-not-knock registries and permit requirements are legal obligations in a number of jurisdictions, and they vary by city rather than by state. The consequences land on the company rather than on the rep, which is exactly why companies care about them more than reps expect.

Check the rules for the city you are working in, not the one you live in. They differ more often than people assume.

Leaving well

When someone asks you to leave, leave, and do so without a parting line designed to reopen the conversation. A rep who exits cleanly leaves a door that another rep can knock next season. A rep who pushes closes it for the company permanently.

Common questions

Knock or ring the bell?: Either, once. The problem is repetition rather than the method. Repeated knocking or ringing reads as pressure and is the most common complaint homeowners make.
How long should I wait before leaving?: Long enough for somebody to cross a house, which is longer than it feels when you are standing there. Then log it as not home and move on.
Is ignoring a no-soliciting sign illegal?: In some jurisdictions, yes, and in others it is grounds for a complaint that costs the company more than the door was ever worth. Treat it as binding either way.

More on door knocking

The craft of working a door: approach, first line, reading the house, what to do when nobody answers.

All of door knocking