It may be the fact that you feel it's a sign that causes your attention to notice that time whenever it occurs. Numbers (including time on clocks) tend to be noticed and remembered when the number has personal meaning, emotional significance, or is unusual in some way.

Determining whether or not a certain number is a sign related to a personal significance isn't in the realm of numerology calculations. But you can read up about the numerology meanings of the numbers you're seeing:

• The number 1234
• The number 12
• The number 34