BN BN Caboose Markings

I've searched the internet and the Burlington Northern forums and haven't found my answer yet. What I would like to know is what the "P" on most BN Cabooses stands for. All my HO and G Scale cabooses in BN have a P on them. I've also found dozens of photos of BN Cabooses with the P on it. But does it have a particular meaning?

 

I'll guess it means "pool", like the P on many UP cabooses.

 

Well considering how long I've searched for the answer, and I have seen it on UP Cabooses too, I'll buy that answer. Thanks so much ^^

 

It does mean Pool service