Math/stat postdoc: how important it is to be a 'named' postdoc?
Very few postdoc positions are endowed, and most of those are at universities that are already very good. As a consequence, the practical implications of being on such a position are relatively small: If you get one, you're pretty much by definition already at a good university, and the delta in prestige is pretty negligible.

What matters are (i) your publication record, (ii) which institutions you've been at, (iii) your letters of recommendation (all not necessarily in this order). What kind of postdoc position (endowed, grant-funded, teaching-supported) you had is not a relevant decision criterion in my experience.