In the last couple of weeks, I have encountered lots of elk and deer on the roads. Two times in the last several weeks I had to wait for 5-10 minutes on the road while herds of elk crossed the highway. This got me thinking about how to signal other riders about this danger.

We have a hand signal for "slow down", but that seems a bit vague. Any ideas?

A big mirror on the inside of your wind shield to reflect that look of sheer terror to those behind you.

I do a rapid tapping of the brakes as soon as I have reached a comfortable speed and I may swing my left arm up and down with my palms facing down, I also do this for approaching riders if I have passed through an area heavy with forrest rats.

The one we've used a couple of times on group rides is to do the 'slow down' wave followed by holding your hand up to the side of your helmet with the index finger pointing up and out, with the thumb pointing in a different direction (think antlers or horns).  Also, sometimes we point in the general direction we saw said deer or cow if there is sufficient warning, to let those behind us know about it.  Kind of like pointing your toe at debris you are swerving to avoid.

This is by no means a standard hand signal, but it conveys the message to approaching riders about livestock or wildlife well enough.

Flashing brakes and or headlamps is my alert for anyone around me. If you're in gear with the clutch engaged, you can hit the starter button for headlamp flash without damage.

I still think they need to move the deer crossing signs to better locations so this doesn't happen

Flipping the highbeams and pointing with both arms stretched. This is the international sign for danger, both sides. pointing to one side means danger on that side.. 

I still think they need to move the deer crossing signs to better locations so this doesn't happen

Please Move The Deer Crossing

I think the worst I've encountered was coming up on a herd of goats the shepherd was moving down the road.  We basically had to stop while they were herded past us.  Some of them got scared and urinated on the road.  When we finally got moving we discovered there was goat scat on the road for about 2 miles.  Not pleasant.  I was just glad I wasn't a fanatic about washing the bike or I would have had to turn around.

I use the left handed helmet antlers and point to the right or left side of the road after I so the road massage. Basically, left palm down like I'm rubbing someone's back then make my hands into antlers. Then point to which side if possible across my chest or straight out to my left.

Basically like someone said earlier on in this thread.