Add the letters TM on the logo. You are permitted to do that without actually registering the trademark. Note the date you started using it. If an issue arises, you can show the date. If the other company registers it, your probably going to have to change it. If there is any difference in the designs the grey fog arises. May the man with the be$t lawyer win. In other words, don't mess with the big boys out there. They can definately afford it. There are catagories for trademarks so they would also have to be in the same industry. Stop worrying and cook up some designs.