Covering up labels on the D300 isn't going to disguise it anymore than covering up labels on a Landrover will disguise it. It's obviously a big digital SLR.
I think hiding labels on a Leica is almost always pointless. Most people don't know about Leica. Someone who does will recognize the camera in an instant, labeled or not.
In other words, thieves who are just looking for a quick way to score some cash aren't looking for particular brands. Thieves who are looking for particular brands won't be fooled by hiding the name.
Mardi Gras is great. Stunningly crowded in the Quarter, with many, many well-lubricated people. Use common sense and watch your wallet.
Hint: If I was going to steal a camera or pick a pocket, I'd hang out along the parade route and make my move when people leap to catch the beads thrown from the floats.