Basically its illegal.
In all of my outfits only a transparent layer of hoar frost on the underside of the wing caused by cold fuel tanks was allowed and nothing else.
I was sent up front by my captain as I was the only pilot dead heading in uniform with a North African carrier.
He had spotted clear ice which our company engineer had missed. The crew had through tankered, they returned to the ramp and deiced twice to clear the ice.
One of our colleagues climbed onto the wing of the aircraft he was dead heading on as there was more than an inch of snow and the crew told him to mind his own business. Aircraft returned to the ramp and he spent a couple of nights in jail. Its not just the Russians that play silly buggars.