Don't put Not For Hire on the side of your truck. Just because you aren't hiring yourself out does NOT mean you aren't commercial. It just implies that you are commercial and hauling for your own business. You are better off without those signs.
As for the 26,000 issue. I called the Michigan Truckers Safety group that works with the DOT and MSP. If I am hauling my own belongings, not involved in anything that may have prize winnings, etc... Then I am NOT commercial. If I haul my Jeep to an off-road rock crawling competition that pays out awards, then by law I am commercial and better have a CDL. Only when you cross that commercial line does the 26,000 pound issue take effect. As long as my trailer is rated to haul it, and my tires are rated to haul it, I can load as much as I want on a trailer and be perfectly legal. However, you may run into super-DOT who disagrees or doesn't really care what the law really says. If he writes the ticket, it is up to you to prove him wrong in whatever state you are in. You are subject to trailer length and overall combination length restrictions as well as posted road weight limits though. It is all very confusing. Watch the speed limits too. Even though I am non-commercial, I still must follow the truck speed limit at least in Michigan. Not that I pay too close of attention to that, just like most of the truckers around here...