Red x on interior walls of REO

[Tim Gordon]

Hello everyone, 

I went to look at a potential investment property today. It is a single family REO with no power or running water, built in the early 1950's. The house was winterized September of last year based on the date on the seal keeping the toilet closed. On a few of the interior walls there were red x's drawn in what looked like red marker. I asked the realtor if he knew what the x meant and he had no idea. Has anyone encountered this?