"@" OR "AT"

[XR250]

I was reviewing a colleague's drawing. For rebar spacing, it showed, "#4 AT 18" O.C." I typically use "@". I feel like it I was going to spell out "AT" I would show "SPACED" instead.
Is there a convention?

Thanks

 

[ctopher]

Is there a standard to follow for structural?

 

[XR250]

Is there a standard to follow for structural?

That is basically what I am asking