This might sound corney.... but I always liked the idea of planting a tree as a symbol of establishing roots. If they have property they aren't renting... then a nice flowering tree might be an option. Of course, you wouldn't want to bring the thing to the reception but maybe a tag or picture with a note and a nice scripture included ....
Psa 51:10 Create in me a clean heart, O God, and renew a right spirit within me.
