Just so you know, all parking garages in California have that same warning posted in them, yet parking garage attendants continue to have healthy children. The operative word in that sentence is "may". The mugs don't necessarily have lead or cadmium on them, but if they're made in a factory where there are other products that are glazed with them they still have to carry the label.
If you're really worried about it, don't wash the mug in a dishwasher or microwave it or use an abrasive cleaner on it. If there is anything on the mug that will keep it from coming off, and don't forget that
biphenol-A has been suspected of having adverse health effects on Humans for years, especially on children ... and they make baby bottles and line soda cans out of it.