Is it a light/beacon or an AN/ALQ-144 IR countermeasure device?
The AN/ALQ-144 emitter has a cylindrical shape with faceted "windows" which are coated with a purplish-red reflective coating. This is usually mounted directly behind the rotor mast, between the engines.
PS: Not sure but I believe it's not often mounted on the SH-60 and is more commonly seen on the MH-60