Two hand signals and a bell

There are only two hand signals worth knowing, and between them they cover everything you need to communicate. A hand held straight up in the air means "I am stopping". An arm held straight out to one side means "I am turning that way". That is the entire vocabulary, and everyone here uses it constantly.

Signalling is a legal requirement, not a courtesy, and the reason is density. On a busy track there may be a dozen people behind you, all travelling faster than you think, none of them able to see past you. Your signal is the only warning they get. Give it in good time - before you slow, before you turn - not while you are already doing it, which tells people what happened rather than what is about to.

Before you signal, look. The order is always the same: look over your shoulder, give the signal, then move. Signalling first and looking second means announcing a manoeuvre into a space you have not checked is empty.

Your bike must also have a working bell - it is required equipment, and a bike without one is not legally roadworthy. Danes use it as a short, neutral warning that they are coming past, roughly the equivalent of saying "behind you". It is not a complaint or an expression of anger, and it is worth not taking it as one.