Incidentally, when writing equations carefully, one should put the variable "voltage" V in italics, and the unit "volts" V in roman. Similarly, italic C is the variable "capacitance" and roman C is the unit "coulombs".
We always used U for potential in school. And you'd be failed immediately if you pluralized SI units, so 1 volt, 2 volt, 0.5 volt. 2 "volts" would be an incorrect answer on a test. Temperature: 273 kelvin, 300 kelvin, 10.2 kelvin. Nor were "colloquial" SI units acceptable, like cm. (The only acceptable colloquial unit was ˚C as opposed to K, when the context called for it.) This is in contrast to metric (which is not quite the same as SI plus colloquialisms) and imperial, where pluralization is expected: 1 lb, 2 lbs. We were also taught never to put a space between values and their SI units or prefixes, but it seems the SI has standardized on a space. Personally I find that awkward since when used in an expression you definitely don't want spaces; for example, when multiplying 1k*50m the k*m cancel and you're left with 1*50 = 50. "1 k*50 m" just looks awkward to me.
Oh, and we were also taught to use uppercase U, I etc for DC: operatings points, bias, etc. And lowercase u, i, etc for small-signal properties.