First of all the rule of threes is great except for in Europe where it is the six, 3 is the reply.

Secondly Signal mirrors can be used on moonlit nights. During WW2 many covert airdrops where made by having the drop zones marked by signal mirrors. I also know of at least three rescues carried out after spotting a signal mirror at night.

Anyone that has tried lighting and maintaining 3 signal fires will know how hard and unpractical it is especially if you are by yourself. One fire will do. Two 12 year olds recently used a fire to attract a S&R helicopter in the lake district. After getting lost in freezing weather. Good skills for 12 year old.