How does a creator of a font know if you are using it commercially?

There are sites on the Web that allow you to download and install fonts. You can purchase a mega pack for a set price and download all the fonts in the pack at once, or do it one by one. Sometimes they tell you at the example of the font if it is free for personal use or for non-profit, or if there is a license if used for commercial purposes. Even those that don’t, once download have a license, or “read me” file that comes with it stating the cost and terms of font usage if used for commercial endeavors. How would the creator of the font know it was used commercially by someone who did not obtain a license if they did not happen upon the Web site it was being used and could recognize it as theirs from the many that look similar? What if a person used it but in signage that never was on the Web, thus giving the creator of the font no opportunity of seeing it if they did not live in the area where the sign was? Or is the license more in keeping honest people honest because it is fairly unenforceable?

(Only because it is not something one can easily Google)