Sakurai: Pic of the day. Here's the new edition of the Ray Gun. The Smash Bros. mark appears backward because it acts like a stamp. We design the Ray Gun carefully each time to ensure it doesn't look like a real gun.
It's also worth noting that Sakurai says "each time" meaning this was taken into account at least even back in Brawl. I think the idea is not that it looking like a "real gun" is too mature but rather that the ray gun shouldn't look like a "real gun."