When you take blood thinners people can get platelets on the skin, some are quite dark, that look like bruises, you may notice them on older people, it is a side effect of anticoagulants. They can come and go depending on how your blood is flowing, as some food and drink also thin the blood, it can be more flowing than normal. Remember alcohol also thins the blood so do be a little careful with that while on anticoagulants.