NumForm: numeral form
Feature of cardinal and ordinal numbers. Is the number expressed by digits or as a word? This feature appears in 10+ tagsets that I studied. Note that it is a bit Euro-centric because it distinguishes (in some tagsets) (Euro)Arabic digits and Roman numerals, but what about digits in various other scripts? In texts in many Indian scripts and in the Arabic script both native digits and Euro-Arabic digits can appear (e.g. 2014 vs. २०१४ in Devanagari).
Word: number expressed as word
Examples: one, two, three
Digit: number expressed using digits
Examples: 1, 2, 3
Roman: roman numeral
Examples: I, II, III