They also mark the northern night sky when the sun is at its lowest point, and were a clear marker for ancient timekeeping.
It was a chill, crisp day, a clear marker for the end of summer and the beginning of autumn.
Often, advertising takes the form of scent marking the territory boundaries as a clear marker for others to stay away.
I shall return to that point later, but I want to put down a clear marker now.
Less encouraging is the £4.9m cost of a 3-month covenant test delay - a clear marker that expensive banking negotiations lie ahead.
He added, "They're going to lay down very clear markers with dissatisfaction about Roberts not answering things they think he could have."
"We have no more clear political markers," said Christiane Laporte, a headmistress.
They had taught us what they felt we could grasp, and had left us clear markers as to their presence.
I regard that as modest enough, and we have to set down clear markers here.
So we need have no fears concerning research, which is a source of progress, as long as there are clear markers to prevent abuse.