The symbol spell describes creating a "harmful glyph" on a surface or within an object. This glyph is described as being
nearly invisible, requiring an Intelligence (Investigation) check against [the spellcaster's] spell save DC to find it.
The glyph is clearly magical, and thus would normally be found by detect magic. Does the above sentence from the spell's description modify that?
If not, does detect magic highlight the symbol of the glyph, or does it just reveal that there is a magical abjuration effect there?
This is relevant for a published adventure:
In Waterdeep: Dungeon of the Mad Mage, Halaster has learned how to augment the symbol spell with additional "Elder Runes", each with their own depicted symbol (which the character's see when activated) and associated effects. If detect magic highlights the glyph itself then the characters can discern the effect (if they have already seen the glyph) without performing the Investigation check.