Why would it be an upper-case "I" for "Identification", when its obviously there solely for the purpose of identification? Why not also "L", for light?
On nautical charts (as per ScottBouch at post #13) all the symbology is relevant in describing the characteristics of the light;
F = abbreviation for fixed (ie a steady light).
Fl (Capital Foxtrot, lower case Lima) = abbreviation for flashing. (a system of digits and characters may follow to define the quantity and duration of cycle).
G = abbreviation for Green; R = Red, and so forth.
Therefore, I suggest; FlR =Flashing Red.