First I want to clarify what dealer's signature not is. If a dealer produces outcomes like long series of Red or Black or any other layout related results that usually catch attention, that's not dealer's signature. It is just impossible to intentionally hit a Red or Black pocket regardless how talented a dealer is. Dealer's signature occurs when dealers fall into their own natural, preferred or most comfortable rhythm when they deal. They tend to spin the ball with approximately the same speed and it will tend to spin around the roulette wheel track the same number of times as it did on previous spins. Same thing needs to be true for the rotor. If both conditions are met the ball will land approximately the same number of pockets away from where the dealer picked up the ball as it did the last rounds.
But it's not that simple. The speed of the wheel's rotor should turn at low to medium speed. Is the speed to high the ball will bounce back from the pockets in unpredictable ways and directions. There are different types of balls being uses in casinos. Heavier ones that have low tendency to bounce a lot work best for dealer's signature. Is this really possible? Can dealers actually have such signatures? The opinion of experts is divided on this topic. A few say it's possible. More say it isn't possible. And no dealer will ever admit in public as long as he wants to keep his job.
I spent about one year watching live casino croupiers spinning in order to learn all the different factors influencing the spin result. After that year my eyes were able to spot if a dealer really spun from the previous number or if he just put down the ball at the track above the previous number and then pushed it along the track for up to a quarter or half wheel before the ball would actually leave his fingers. I could even tell after two rotations of the ball if the ball or rotor were turning slightly slower or faster than the round before. Having developed those skills, it was easy to identify dealers with signatures and take advantage of it by betting 10 to 15 neighboring numbers at the wheel. Using the race track at online casinos there is no problem to place the bets within one or two seconds. But I never tried to do this in land based casinos because to me it seems impossible to place that many straight up bets at a crowded table unless the croupier accepts sector calls. But after a few wins he would know what I'm doing and intentionally change the way of his spins. In these days you can't find any online casinos that let you bet after ball release. Maybe too many players took advantage of that dealer's signature because all conditions where changed by the casinos. Now rotor and ball speed are intentionally varied every round and it became almost impossible to find a dealer's signature. If a ball lands in the same sector two or three times by accident you can observe that the dealers spin rotor and ball so hard in an attempt to end that series. And that is proof enough for me that casinos are well aware of dealer's signature and that they educated their dealers about it and the dealers get instructed to vary their spin speeds to a maximum. A dealer's signature happens unconsciously which means that the dealer is really not aware of what he or she is doing. But I'm confident that many experienced dealers have the ability to willingly manipulate where the ball lands in respect of wheel sectors in the range of 5 to 10 neighboring numbers.