"Oh, yes! Actually, wait just a moment, I can check this. Look out forward, and I'm going to send out a signal."

If she sends it straight up, it'll harm nothing and fizzle out on the way down, and the sending stone will catch an offhand "ignis" before a streak of a little mote of fire shoots up from not too far off. It dissipates without a target, in the open air, but it's a sign all the same.