I've no idea what, if anything, is the symbol for a 4-20mA sensor. A current source makes sense in my head at least.
I guess if it was drawn correctly the + and - wouldn't actually be around it at all, the diagram only needs to show the 12V source and ground.
The documentation however only gives the electrical connections in terms of a + and - so it's good to have for reference.
In other news, 250ohm resisters ordered, I was shocked at how they start at £5 for such a tiny component. 0.1% tolerance and a specific use market do that i guess.