Standard engraving includes any character on a standard US English keyboard, plus the heart icon (♥ solid or outline).
Length of engraving depends on ring size, ring width, ring style, and size and position of print.
Rings with a wrap or tip print on the outside can accomodate about 25 characters, including spaces. Rings with a tip print on the inside can accomodate about 12 characters and spaces.
Dates can be engraved in whatever style you prefer. Some examples:
January 1, 2015