As the text states, some people may turn off signatures, if you post inside the signature divs, some people will not be able to see your node.
As a solution, there is now Node Template in User Settings where you can specify a default template for your node (info)
I took care of the warning by placing a single <p> tag in my node template, so everytime I try to compose a node, I have a starting tag waiting for me, and no warnings.
He who asks will be a fool for five minutes, but he who doesn't ask will remain a fool for life.
Chady | http://chady.net/