In the UK I've found a raised leg to be recognised in both English and Irish sessions pretty much everywhere. It usually means "finish", but can also signal a change of tune. In these genres it is not usual for people to take solo breaks, so we don't need a signal for this.

In a large session, making eye-contact with everyone in the room can be next to impossible. A clearly visible signal or call is preferable. Most players have both hands occupied and not all instruments are appropriate for signalling with, so a raised leg is easy and widely understood.

In a smaller session, especially where the musicians are used to playing together, eye-contact or other more subtle signals may work.

On stage, my band usually relies on eye-contact or sometimes a call.