Your actions will most certainly be mistaken by local law officials. A soft brush. The kind you might use to polish your shoes work well. A tooth brush is also a good thing to bring. Paper, White or rice paper works best.
Rice paper has a really nice feel to it and can be surprisingly strong.
Tissue paper that you put into gift boxes also works well. Black or gray chalk or charcoal crayons. All of thers can be messy but if you're careful it makes a very nice texture. Flat black crayons and rubbing wax are the most common. Scissors or exacto knife.