Michigan checking in. Usage is governed by Public Act 300 of 1954
(Michigan Vehicle Code), as amended. It specifically outlines which types of vehicles may exhibit flashing, oscillating, or rotating lights, under which circumstances they may be operated, who may operate them, and which colors may be used for which purposes. It's similar to Nebraska law in terms of who may use what types (though fire/EMS/doctors are red only, blue is for law enforcement only--I know it's opposite in other states). A private motor vehicle may be classified as an "Emergency Vehicle" under very specific circumstances (§257.2), and are only allowed to operate as such with specific drivers, under very specific conditions, upon authorization, and [by my experience] with State-recognized emergency vehicle operator training (EVOC) being successfully completed, including a closed-course practical component. Pre-emptive devices like the OptiCom are also included in these restrictions per §257.616a.
Interestingly enough, the law is not lax on who may posses amber lights. It is specifically called out in §257.698, and though I am not a lawyer, I cannot see any language that would permit their use in the course of storm spotting (at least in MI). Enforcement
is a whole different matter, though (there are plenty of folks who have them and operate them in inclement weather).
In the early 2000s, I had a red light on my personal vehicle that I used occasionally when responding to incidents with my FD. It had to be approved by the fire chief, the vehicle had to be registered and undergo annual mechanical inspections, it could only be used within and no more than 3 miles out from the borders of the municipality I worked for, and I had to have EVOC recertification annually (no big deal since that was also a job requirement). These were department requirements, not necessarily state laws. The light was removable though, and I never
took it out of state. I eventually did away with it, and started working duty shifts, where I could take the "company cars" on incidents, which had all that stuff pre-installed and legal. My current vehicle (that I chase in) has no flashing lights of any kind, unless you count the 4-way hazards. I'm a pretty low-key, chase-under-the-radar kind of guy (bad pun not intended).
Here's a link to the MI laws
. It's a local municipality's site, as the official MI legislature site is down. Because of course it is.
EDIT: There's also this thread
that Dan started a while back. Covers 2 more states to some degree.