The symbol harms those who trigger it (usually those who pass over it, touch it, read it, etc.) ... To be effective, a symbol must always be placed in plain sight and in a prominent location. Covering or hiding the rune renders the symbol ineffective. ... As a default, a symbol is triggered whenever a creature does one or more of the following, as the character selects: reads, touches, or passes over the rune, looks at the rune, or passes through a portal bearing the rune. ... In this case, "reading" the rune means any attempt to study it, identify it, or fathom its meaning. Throwing a cover over a symbol to render it inoperative triggers it if it reacts to touch. To trigger a symbol, a creature must be within 60 feet of the rune.
