Anyone got any idea what the staining in the picture attached could be?
Picture doesn't do it justice but it is very prominent.
Called in by a letting agent as the tenant left it in a bit of a state in a virtually brand new property, including the red staining as per picture running either side almost the length of the lounge door only

Letting agent said the tenant told them it was to do with the door bar and nothing to do with them (but they would wouldn't they :

)
Explained to them I've no idea if it will come out until I try as I do not know what it is but they've asked for a report to give to the tenant.
Any ideas?
Thanks
Paul