My D2B says 54 kts. The standard does not fix a given speed.
IN

My SZD-55 says 56.7 kts/105 kph.
CS 22.1545 Air-speed indicator (See AMC 22.1545)
Each air-speed indicator must show the following markings:
.... some deleted ....
(e) a yellow marking (triangle) for the lowest approach speed (at maximum weight without water ballast) recommended by the manufacturer;
2D