I don't know, Gaze attacks might be the right way to do this....setting up a slightly expanded option with them.
The Symbol spell details looking at the rune and reading the rune as two seperate things, altho the text of the spell states “...'reading'” the rune means any attempt to study it, identify it, or fathom its meaning."... which does not neccessarily mean spending an action.
So, using Gaze attack as the rule to work with:
Upon entering the range of a trap triggered by either sight or reading, the character is subject to a Gaze attack and must succeed at a Will Save DC 15 + the traps CR or trigger the trap. {spell trap CRs are generally based on 1 + spell level}
If the trap is triggered by reading it, a character must succeed at a Will Save DC 10 + traps CR or trigger it.
A character actively searching the location of the trap or reading a text containing a trap suffers a -10 penalty to this save.
Sample: Symbol of Sleep, CR 6 {Spell level 5 + 1} has a Gaze DC 21.
My 3rd level Half-Orc Druid, with a Will Save of 6, will almost certainly trigger this trap.... it is a CR +3 encounter after all.
By the time he is 6th level his save will be up to 8. He will have almost a 50% chance of not triggering the trap....about right for a CR equivilent.
End result: No more 'do you look at it' back and forths. Since a character knows when they are subject to a save, they will get to do the search thing where the trap is instead of creeping along while looking through mirrors.
RBDM's wont tell them what kind of save it is, so the character may well search the area and trigger the trap anyway.
Symbols lose a bit of power as the character now has to fail *two* saves in order to be affected
RBDM's can still get around this by setting symbols into areas that need to be entered and searched
Also, you have a means to search the area without triggering it that is already documented in the RAW... use of mirrors. There are also clear rules on when the PC decides to 'avert thier eyes' from the big glyph thing on the wall while walking past
{at least once when I say 'RBDM' I really mean 'intelligent and cunning NPC wizard'

}
Finally, this also means that the odds of the big dumb fighter type walking up to a symbol and saying 'whats this?' is pretty high
