You might already know this, but I found this in 5 minutes on a Google search for ARMN reporting marks.
As for ARMN marks- the reason why UP uses them on their refrigerator cars is because they own the reporting marks. ARMN was the American Refrigerator Transit company's marks for their mechanical reefers- ART was owned jointly by Missouri Pacific and Wabash (later N&W). N&W sold their remaining stake to MP in the late 1960s which gave MP control of the ARMN mark. UP then acquired usage rights to the ARMN mark in 1982 when they merged the Mopac. The UP decided to ressurect the marks when they began rebuilding and re-equipping their mechanical refrigerator fleet. Former UPFE cars rebuilt at Pocatello, ID and newly built reefers are all receiving the ARMN marks now.
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Maybe someone else can provide more information.
