There are a lot of up-datable ESC's that have the option to run dynamic timing to the motor to get more top speed out of the car on a gear ratio that allows a lot of acceleration off the corner. These days, this is referred to as "boosted" racing.
Those same ESC's usually have a no-timing mode, and for easy tech they will have an LED, or series of LED's that will blink at neutral throttle to show they are in the spec no-timing mode. This is commonly called "blinky".
There are also some ESC's out that have no timing modes built in, and don't necessarily blink at neutral, but are still legal for "blinky" racing.
A list of the ESC's that are legal, or can be configured to be lega, along with whatever LED display they should have, if required, for Blinky can be found here: