I less than four minutes a crook can steal your check, selectively erase your writing, and make the check out to himself for any amount. That's checkwashing and it's preventable.
Most pens use dye, not pigmented ink. The uni-ball® 207™ uses ink with certain color pigments that bond with the paper fibers in checks making it very hard to "wash" the ink off. This pen, and others like it, could be a simple defense against the threat of checkwashing, which is simple and fast to do. The use of a pen like this, combined with the habit of properly filling in all the blanks on each check, and routine audits of bank statements will help you defend against checkwashing.