Seems like a supremely bad idea. Especially the single quote and the space. You're going to be referring to those properties in Lucene query strings and as keys in an array (e.g., in JavaScript, like this: doc.properties['globalscape:fooProperty']), in properties files, in XML, and on and on. So keep it simple. Those symbols add nothing to the descriptiveness of the property that you can't accomplish with plain text.