I am making a logo proposal to a possible new client. How do I keep them from stealing my logo designs I present to them?

You are automatically protected by US copyright laws. You own your artwork and as long as you have not transferred the rights to the designs to the client, you still own them. The only thing you can really do to protect yourself is to place the copyright symbol on each logo and state that these logos are property of your company and may not be reproduced without your permission. If they take your design without paying, then hire an attorney an go after them. One other thing to consider is not doing this type of “spec work”. You are opening yourself up for someone to take advantage of your hard work and not pay you for your ideas. Many clients try to get ideas from designers and go other places to get the work done cheaper. Your portfolio should be enough to let the client know you can do the job. However, I understand that there are times that you need to do this to land a big deal, just be careful.