Hello ITineris,
Thank you for your contribution in term of notes as well as edits.

The markings that you are describing here are forestry markings. They are used by the forest management to document limits between forest sectors. They are always red and will take the form of: horizontal/vertical line, 2 lines, dot, H, or the ones that specify the number of the sector have also white between the red lines. 

There is little importance to those if you are not part of the forestry team, people hiking are mostly ignoring those, I also cannot find any information about mapping practices on those kinds of signs and any mapping of those would be incomplete without a large survey of import.

I hope you understand why I choose to chose your notes and if you have any questions of additions don't be afraid to contact me.