Can you help me find material for glass appliques?

I have a customer (a head shop owner) who wants to put custom lettering and art on the plain glass water pipes she gets. She showed me one that was pretty generic. The art felt kind of like very thin tar shingle that had been melted onto the glass. All the negative space between the lettering was just the glass, not a sticker.

I have a Roland plotter, what I need is to know what kind of material this is. It needs to stand up to repeated washings. I can’t find anything with Google even, because I keep turning up stuff about stained glass and etching. Can anyone help?

Do you mean like this?

No, I need something that can take a scrubbing in the sink.

From the linked page: Peel the cling from the plastic page protector once the paint has dried thoroughly. You can stick it to any window, mirror or other glass surface, and reposition it anytime you like.