What do the “T”, “T 25”, and the lower-case Greek sigma on my watch dial mean?
These are optional industry markings, found next to the inscription “Swiss Made” on some watches, which signify what the markers on the dial are made from. The “T” means that tritium (a low-level radioactive substance) was applied to make the hands and/or markers glow in the dark. The “T<25" means the same thing, except it spells out that less than 25 milliCuries of radioactive material is used. See section 6.1 for more information about Tritium. The lower-case Greek sigma means that the markers are made of solid gold.
