ACCESS 2003 Security Warning

I have read through the various posting regarding ACCESS 2003 security warnings. As like everyone else, I receive a security warning stating, “This file may not be safe if it contains code that was intended to harm your computer.” I have already installed Microsoft Jet 4.0 Service Pack 8 and I have already enabled sandbox mode. This warning still appears when I try to open databases sent to me by other people. It also appears when I try to create a new database from my own computer. I understand why this message may appear when I open other peoples’ databases, but why would this error message appear on my own computer after I create a database from the very same computer? I would like to market my databases to specific clients, but I need to eliminate the security warnings that would appear each time they opened my databases from their computers. I don’t want to suggest that people change their security levels to low in order to open my database. For this reason, I am considering the option of digitally signing my databases with an authenticated signature. As something like this would run anywhere up to about $400.00, I want to make sure that it would be the best, and correct, option for me. My ultimate question: If I am already trying to create databases from my own computer and receive this warning message, would a digital certificate work in eliminating the error message for my future clients? Also, I understand that I may use the signatures for up to a year. Would I be able to use this for multiple databases that I create as long as it’s within that one year, or would I only be able to sign one specific database and use that same database for the entire year? This is a bit of a pricey endeavor for me, so if there are any other options, I’d love to hear those, too. Thank for the help in advance!