It means you do not have to remain at 250kts or below whilst on the SID, and can accelerate now, or whenever you want. You do not have to, but can if you like
....and of course some aircraft - esp A340s - even
slow down/remain very slow when NO SPEED is given, to give a better ROC. At least one nice little video on the safety booth-kiosk-thingy showing that one!