I do remember intentionally memorizing serial numbers / signs so I could look away and then look back to see if they changed. And they did.

However, if I am looking at the object with the text on it, and do not look away, it does not change and is usually legible / makes sense.

The only time I have problems, is reading out of a multi line page, such as in a novel or something like that. It can get really confusing.