RG-21 Vertical Height/ Height Restriction Signs, also known as RG21, RJ22 or a R5-4 sign, show the safe vehicle height in metres for each specific site displayed on the circular vertical clearance sign. RG-21 Signs are used below a PW-47 Overhead Electric Cable Sign (also known as a PW47, WW41 or a W13-5 sign) to form a LOW OVERHEAD CLEARANCE AT ELECTRIFIED RAILWAY CROSSING sign combination.

RJ21 = One Decimal
RJ22 = Two Decimal