Show in-game indicator that some players are in Vigilant Mode

**Is your feature request related to a problem? Please describe.**
Inspired by #5259, which discovers/reviews "Vigilant Mode".

There is currently no way to know whether someone else in the same map is in Vigilant Mode.

**Describe the solution you'd like**
There should be an in-map indicator to show that a player is in Vigilant Mode.

For example, if disconnected players gets a Sleeping emoji (💤), then a Vigilant player should e.g. get a Police emoji (🚨). Players will be aware someone may be cheating.

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
It's an information game; perhaps I should not talk too much.

**Assignment**

- [ ] I'd like to be assigned to this issue and work on it myself

Start by tracing the existing sleeping-player emoji and reviewing #5259 for how Vigilant Mode is detected. Identify the in-map player indicator entry point, then make Vigilant players visibly distinct with the agreed emoji or equivalent and verify it appears to other players in the same map.

Written by the indexing model from the issue text.