I would make him sign the box. I think it far more valuable to let your system bundle stayed sealed. Generally, sealed items net more value and it might be a collector item in near future. You should avoid making him sign items that might potentially drop in value like common game or system. If msrp goes down, so does your item. People who had their signed ps3(from Metal Gear system bundle) have a hard time recoup their cost when ps3 msrp went down.