I sadly don't really get to use Symbol spells a lot, since as adventurers we rarely defend a place. But I like them, so I tried to think of a legal way to bring them into a fight.
As per spell description it can't be used offensively directly (like putting it on sword and then hitting someone).
So I thought I could put a symbol on my shield, using the trigger condition: If I lie my shield flat on the ground and step on it with my feet it activates.
After that I could pick it up again and have it radiating the effect.
Is this a legal usage of the spell? I thought about putting the healing Symbol on it for emergency healing (if made permanent it is a free group heal every 24 hours for 10500 gold).
You know, I don't see why not. Nothing I've read says that the symbol's surface must be immobile. As a bonus, if your shield gets sundered, hey, one last heal before the spell goes bust.
However, you may want to check the wording. It's probably inadvertent, but because symbol of healing inherits most of its language from symbol of death, you are immune to your own symbol and cannot trigger it. So you might have to attune it to someone else stepping on it, or maybe a password that triggers it. And it'll be more useful to the party than yourself.
That's how I read RAW, anyway.