For me as a magician I used to think that spectators will think that I have tricks cards if I use a Split Spades deck or a Ghost deck but lately I don't think this is the case. For me I found that nobody really cares about how the cards look and never ask to examine the deck. I think that people who have never seen magic before (so most spectators) will not think that the custom deck you're using is a trick deck because they are enjoying the experience and not caring about the cards. Also most spectators rarely ever use cards in their daily life so they don't really know what the "standard" deck looks like. Also someone on this forum also put it like this: If a friend got a deck from Disney and used for a game, nobody will scream out HE'S USING TRICK CARDS. No they would probably ask how was Disney. So my point is I don't really think that a different back design will make spectators think that you are using a trick deck.