One of Salesforce CRM’s coolest features from a “bright shiny object” standpoint (i.e. something that aids productivity but also looks flashy) is the image formula field. Jamie Grenney first wrote about this a while ago, and his pdf and sample images from the Salesforce built-in library are available on the community site.
Sometimes, however, we want something simple. Sometimes we want to create a formula field that displays a simple checkbox (or an empty box). This is currently not possible, but has been suggested as a Salesforce Idea.
Until that is built into the platform, feel free to use these two images in an image formula field (storing them in the documents folder):
Or download this zip file and put it into a static resource for use in a Visualforce page.