Means the same as the phrase, "
just to be sure"; the "it's Westinghouse"
part originated from
television commercials for Westinghouse Electric in the 1950s, who's catchphrase was, "You can be sure, if it's Westinghouse".
{Craig}: Hey Paul, did you remember to charge your wheelchair
today?
{Paul}: I think so but let me
check just to be sure it's Westinghouse.