Dilbert refers back to a worker who was fired for posting a Dilbert strip on a bulletin board at work. Dave Astor's got more details than I can bother with.
Baldo's creators tip a hat to Gus Arriola, the cartoonist for Gordo who died earlier this month. R.C. Harvey's book on Arriola and Gordo is still in print and is probably the easiest to find if you want to know more.