i know you're mad - i would be too - and like i said, id find the grave with the wreath on and leave bunch of cheap flowers there with a cutting note - and hopefully shame and embarrass the thief.
but as someone else said its the thought that counts, and thats why the gesture for the thief's loved one, is pointless - because a stolen wreath is meaningless, and offensive - placing flowers on graves is not about making the grave look pretty, or showing others how generous you are by getting the biggest showiest bunch - its an act of love, a gesture of care - obviously something the thief doesn't realise or care about.
it would mean as much as just not bothering at all