A small emergency strobe worn on top of your pack or on the shoulder of your outer clothing at night is an excellent and highly-visible distress signal. The pulsating pattern of a strobe is unlike any other type of light source, so searchers seeing it will pay attention. It's much more noticeable than a flashlight, because it is omnidirectional and REALLY bright.
I recommend the ACR Electronics C-Strobe Personal Strobe Light and have this piece of equipment attached to my personal flotation device (life jacket) when boating to show my location at night, in case I fall overboard. But don't think this is only for boating — it's a great dry-land visual distress signal as well. For about $30, you can buy it at West Marine stores (or their website www.westmarine.com). Or do a Google search for other online outlets.