Shark warning?

You're standing on the beach and just spotted a fin cruising near to the line-up. How do you get the attention of the ou's in the water to give them a head's up to get their leg's up? Screaming like a banshee doesn't always work cos if the surf's biggish or the guys are sitting far out, they aren't gonna hear you no matter how loud you holler.

Waving your arms about like a spastic chicken just conveys there's an issue, but isn't necessarily interpreted as being a shark warning. You could be yelling at your grom to come in, or to tell some guy his cabbie has just been broken in to, or a whole host of other things. 

Take this weekend for example. CarPark John and a few others were trading peaks on the wildside, and a crew walked down the beach after having surfed another spot further up and started waving wildy at them. John and the ou's reckoned they were just trying to tell them that the peak they'd surfed was better - and that they should move down there.

​Nup. Turns out that whilst Merv was on a wave at the other peak he got dropped in on by a finned local, and after a stare down Merv decided to give the wave to him and call it quits and go home.

They finally did get the message across about the friendly fin in the area to John's crew, but it took a bit of time getting lost in translation.

So how do you specifically indicate "SHARK" to those in the line-up?

The dive sign for shark is to put your hand vertically on your forehead to resemble a fin. Which works fine when you diving and the ou you signalling to is a few metres away. But there's no ways you'll spot something like that from the line-up over 100m away. 

Reckon the best bet would be to raise your board over your head and wave it about like the guys in the shot above at Ballina beach in Aus, a super sharky spot. At least anyone who's read this will know immediately what it means then if they see waving boards!

​If you don't have a board? How about making a triangle shape using your arms to try mimic a fin? Also likely to get lost in translation.

Any better idea's out there?