250KT IAS BLW 10000
Found the reference in AIP ENR 1.1 - 102 "Aircraft Speeds."
Applies to IFR and VFR a/c operating in Class C,D,E,GAAP and Class G airspace.
Interestingly, the speed restrictions shown for VFR a/c in Class C airspace and IFR and VFR a/c in classes D,E and G airspace are not applicable to military aircraft.