On the plastic lid of a cardboard drinking beaker manufactured by Huhtamäki are the abbreviations L, NG, OT and Z, each with a little spherical knob next to it. What do the abbreviations mean, and what are the knobs used for?
The knobs are so that the servers can depress them, and keep track of what is in the cup.
For example, on the web, I can find a picture of a lid which has knobs labeled diet, tea, cola, other. When a server fills a cup with tea, they depress the knob labeled "tea" on the lid so as to make sure the customer gets the correct cup.
I have no idea what L, NG, OT, and Z are, though. They don't really sound like English abbreviations for various drinks.