Whether its shown alpha or numerical depends on your provider and how they respond to the request. Some networks do have a mode which would disguise it, and some ppl use what are called bounces. Honestly tho, there are more important and useful things to do to protect yourself than worrying about what your mask shows.
-keep current with windows updates/patches
-keep current with updates on any apps you run
-run a firewall
-run 2 or 3 virus scanning apps on a regular basis
-dont type everything ppl tell you to
-use caution about clicking on urls, many are infected
-dont accept files or scripts from strangers
you can find some useful resources at
http://zine.dal.net/previousissues/issue19/resources.php