Abstract: A marker lamp comprising a housing and a lens. The housing has an opening into which the lens extends. An O-ring is positioned in a circumferentially extending groove in the opening of the housing. The lens has a cylindrical portion that extends into the opening which has a cylindrical surface that is engaged by the O-ring. The cylindrical surface has a length in a direction of the axis thereof greater than the width of the groove in the housing. The lens also has circumferentially spaced axially extending projections on a portion of the lens that extends axially beyond the groove.