Hello.

By siren you mean? Normal police sirens or just car horn sound?

the police cars and vans use an entry in their config like this:

weapons[]=

		{
			"policeHorn"
		};

the boat does not.

So you were meaning the horn. Well in cars and vans it makes sense. Not sure about the boat. What use would the horn have for a boat of that size? We are ware that boat horns exist, but the most commno boat horns are used on larger ships which the police one is not.

https://www.youtube.com/watch?v=4nU_0MY-YpM

That is a siren not a horn. Are you by any chance using a mod to add police vehicles? Because the Van and Offroad vehicles that can have police beacons do not by default have a function that enables a siren.

"policeHorn" is vanilla and it is a siren. the police car and van use it by default (instead of a horn).

push

Indeed, the siren on police boats has a place. How nice that it is very easy to implement, we need next actions:

1. in CfgVehicles → Boat_Civil_01_base_F → Sounds add this code see Pastebin
2. in CfgVehicles → Boat_Civil_01_base_F → UserActions add this code see Pastebin

Look at the result - https://youtu.be/Z3Sr42D0J1g, same as @madpat3 requested via video

Police equipment (beacons) animation condition check allows successfully apply the siren feature just to a police one, not a civilian/rescue boat