Aftermarket Horn

'Sound' advice (groan).

I'd forgotten that these things always used to have an adjustment screw...

 

Now there's an idea. I could use Ta-daa air horns to properly confuse people - that would really stop them in their tracks...

 

Here's a comparison of two types of Hella Horn that seem appropriate and are apparently very loud. The sharptones are smaller, so easier to fit but imho, the supertones sound a better fit for a high performance bike.