Once you place the symbol on your map, what you can do is the following:
Ctrl click on the layer with your symbol.
This will make a selection of the symbol layer.
Press the "m" key (for marquee selection)
Press and hold the alt+ctrl keys while moving your symbol. This will effectively make a copy of the symbol, placing it on the same layer.
Lather, rinse and repeat. If you need to adjust the placement of your "new" item, immediately press the "v" key and nudge it into place.
If you have more than one symbol, you can also marquee select the symbol you want, then press and hold the ctrl+alt keys. This will only copy the selected item on that layer.
Makes populating a city with houses that much easier.
Note, if you want the item to be an a seperate layer, follow the steps above, but press the "v" key (for move) instead of the "m" key.
I hope that helps you out.