Say you want to note down a number to another person, and want it to be unambiguous (perhaps the other person is an alien and has more than 10 fingers or something). So if you say
12345, base 42
That's not enough because they will ask
is 42 in base 42 or in base 10
What is the commonly accepted approach here? Should you specify the base in base-9, because that base's representation only has one digit?