When I go to visit the cemetary on the day of the sheloshim, there will not yet be a matzeviah up. There is only a small wooden sign marking the grave’s place. Can I still light a candle and place it next to the sign?
Usually people don’t light a candle there at that time, most probably because the candle with get blown out very quickly. However if you want to try putting a candle there I don’t see why you can’t.