Crud Stuck To Black Exhaust Header

After my ride last week the bike got chucked straight into the bike shed.
I took it out to take me ‘newbie’ photo yesterday and there is a baked on brown splodge (not that!) down the front of the header. Obviously something flicked up by the front tyre.
The Triumph Accessories page implies the pipe is stainless steel powder coated matt black.

Any suggestions on a safe way to remove it without destroying the paint finish?
I’ve only tried gently wiping with soapy water so far as I’m scared to go further without advice.