At Narita Airport on the terminals there are big digital numbers visible from the runway. They aren't in some reliable order- I saw 98,91,93,95,97,99. Maybe they are Aerobridge numbers. I didn't get a photo as I only had my mobile which was off during taxiing. What are they for?
A good way to answer questions like this is to look at the Aerodrome Chart
As newmanth answered, these are gate numbers.
Using Google Maps, you can also see these numbers painted on the taxiway as a guide to taxiing pilots
If you want to understand airport air-side signage, one document I found useful is CAP 637 Visual Aids Handbook. It is a UK CAA document but I expect most of it applies in other parts of the world.
The CAA refer to stand numbers, as far as I know these are the same as gate numbers. They indicate parking positions for aircraft at airport terminals, these are places that allow for the loading and unloading of passengers.
Airliners arriving at airports will know what gate they have to taxi to, and ATC will provide them with taxiway routes. Airports provide signs so that pilots basically know where to find their allocated gate.
Without seeing a photo of what you are referring to, I can only guess as to what the numbers were. Most likely, they were the gate numbers. At Narita, the gates are numbered odd on one side of the the terminal and even on the opposite. Here is a diagram of terminal two, which is what you were probably looking at. At commercial airports, gates are numbered on the outside (in addition to inside the terminal) so that both ground handling staff and pilots know which gate they are at.
Here is a picture of a terminal at Denver International Airport. Note that the gate numbers on on both the passenger loading bridge as well as the exterior wall of the concourse: