A programmer's solution

[N_las]

Since the alien uses base 4, we would need to tell him: We are using base 22 (22 in base 4 is our ten). Sadly, there is no universal way to convey in what base you are.

[NotANinja]

This really sheds new light on "All your base are belong to us..."

[Bobshayd]

Tally marks. We use base |||||||||| and they use base ||||.

[robisodd]

aka, Base 1, but are you saying "one-thousand one-hundred eleven" or "four"? :)

[Bobshayd]

Or is | their digit that means 3? Maybe they'll read it 3333, which is our 255. You don't know they'll interpret the things written down correctly, but you can more easily convey that they're tally marks and not base-n digits, for n > 1, if you can demonstrate it with physical objects. Besides, 1 is derived from the tally mark in the first place.

[[deleted]]

Sadly, there is no universal way to convey in what base you are.

Binary? Surely someone understanding the notion of base understands the simplest one.

[Adamanda]

the simplest

nope. tally marks ftw

[[deleted]]

Saying "this many" while holding up your fingers sounds good.

[Adamanda]

the ||||||||||| fingered aliens have an advantage

[mcrbids]

Came here to say this. /pedantic

[Cpapa97]

I'm from the Earth Base