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.


Symbol can be found by detect magic or an investigation.

The sentence cited provides a method of detecting the symbol. Providing an additional method of detection does not preclude any other valid methods such as detect magic.

Different information yielded by each discovery method

Investigation reveals the symbol

A successful investigation finds the symbol directly, but does not necessarily tell the character that it's a symbol. The fruit of the investigation is discovering the "nearly invisible" harmful glyph.

Detect magic reveals the object it is on

The use of detect magic could lead to an investigation check, but it does not immediately inform the caster that a symbol is the cause of the aura.

see a faint aura around any visible creature or object in the area that bears magic

For example, a book that contains a symbol on the inside cover or one of the pages would have a faint aura around it when detect magic is cast.

Published Adventure Mechanics

Mechanics of particular adventures, dungeons, or stories are instructive as to how to run that particular module. They are not general rules. It sounds like the custom symbol of the adventure provides a mechanism to discern the effects.


Symbol is found as a magical effect, but specific spell and effect is normally not

For a standard symbol glyph, it is can be mundanely found via an investigation as you've quoted above. There may be an action cost for this depending on your DM, but there is not a resource cost. Failing the check will result in failing to find the symbol.

Detect magic provides a more foolproof method, but there is a resource cost. The spell will:

...sense the presence of magic within 30 feet of you. If you sense magic in this way, you can use your action to see a faint aura around any visible creature or object in the area that bears magic, and you learn its school of magic, if any.

Nothing in there states that it provides information on the effect - only that there is a magic present and that it is an Abjuration effect. While that may seem minimal, simply knowing where it is helps creatures avoid it's effects if they can avoid the area (if they surmise that it's a symbol or they think it's some other negative effect.)

The published adventure gives you more information

As you've quoted in the spoiler, there is an opportunity in that case to learn more about the effect based on the additional rules about that particular symbol.


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