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.
{Paul}: I think so but let me check just to be sure it's Westinghouse.
by Telephony July 29, 2014