It is an unfortunate fact of life that theft of beehives occurs and is becoming more common.
When I started keeping bees I decided that I would brand every item, even frames, and as I was intending to have many hives I thought that it would be a good idea to make a purpose built device, based on a gas torch. I am a resourceful sort of chap and I made the brand itself from a chunk of copper 80 mm x 25 mm x 10 mm and formed my initials "DAC" in relief, but mirror imaged, by using an engraving machine. I used "fridge magnet" children's plastic letters to make the engraving template and I used a reduction of four to one on the pantograph.
The picture at right shows the torch which screws onto a butane gas canister... A flame spreader is used to match the flame shape more nearly to the block of copper that it is heating. I was concerned originally, that copper may oxidise at such a rate that the brand would deteriorate, but after 25 years or so use, it produces just as crisp a brand as it ever did.
I usually burn the brand about 1 mm deep so that the depression will show up even if the wood becomes bleached. This frame top bar is typical of the results.
This brand has been exposed to the weather for about half, of it's twenty years plus, lifetime. All traces of the carbonisation have gone, but the message is unmistakable.