What are the Ts for on highrise buildings?

Dear Matt:

I work in a highrise downtown and on some of the windows there are these Ts on the outside of the glass. I look out the window to a nearby high rise, and that building has them too. I've worked in five buildings downtown, and they all seem to have them. They are either white or yellow and always a capital T. What are they for?

-- J.B., Pt. Loma

They are for keeping away aggravation. Aggravation from building inspectors. All those highrise windows have to be made of tempered glass -- glass that's extra strong and shatters into little lumps instead of lethal shards if it's broken. Each pane of highrise glass must be marked with a T to show that it's up to code. Just lost that big sale? Because of the tempered-glass law, you can throw your phone through the window with little risk of cutting your jugular.