Are you sure its a scab and not a retained tail tip or even as a result of several retained tail tips the end of the tail has died?
I know Duke has a different colour on the very tip of his tail and it feels very sharp and pointy and stiff but its normal its just a scale. Without a good picture though its going to be very difficult to work out what it is.
I'd suggest checking his next shed for his tail. Margwar spent a couple of sheds not shedding his tail, it looked kind of scabby, then with a good shed it all cleared up, and touch wood each shed has been fine since.
It is as you describe i said scab as it was the best way i could describe it. It doesnt seem to get any worse should i try remove it
I described several scenarios that it could be, if its retained shed then you can try remove it, if its dead at the end then no leave it well alone and consider a vet to ensre its not infected etc and if its normal as a royals tail is normally then leave it alone.
There are other options though, it could be scale rot and may be present in other areas along the belly. It could be that the snake has climbed the bulb guard and its tail has passed through the mesh of the guard and burnt on the bulb. If you could take a clearer picture it would greatly help or seek the opinion of your local reptile shop, ask if they can take a look.