Plus Sign on a doctor shop

Neha played with bare feet in the sand pit in kids' play area and had a cut underneath the middle digit of her right leg. Not wanting to take a chance around contamination of the wound with tetanus bacteria, I took her to a doctor nearby and he gave her an anti-tetanus injection. I could see a glimpse of my grown-up & shy neha there. This was the first time we went to this doctor and so neha was shy to cry when he gave the injection. She tried her best to hold back the tears and remained silent when he asked did it hurt her too much. This is the same neha who acted like kalpana for a previous injection! I felt sad in a way cos she is already choosing dignity over her kiddish behavior. Maybe its a transition that I should get used to. My T-shirt slogan would not be "18 till I die" but "35 till I die cos then my daughters stay at 4"

On the way back, she was her inquisitive self and asked me - why do doctor shops have a symbol of "one standing line & one sleeping line". That took me off guard and I had never wondered what the plus sign on a doctor shop meant. I googled around for a while to look for meaning of the usual medical symbols. And found out about two of them:

Rx
The symbol "Rx" has two representations. It is meant to signify the eye of Horus (Egyptian god for light, sky & goodness) or it just means prescription (take this). So its either a god's symbol to wish good luck or a direction to take something to get well.

The symbol of staff with two snakes coiled to it:
It is the staff of Aesculapius (also called Asklepios), the ancient mythical god of medicine. His Greek name was Asklepios and his Roman name was Aesculapius. In reality, Asklepios may have once lived and been renowned for his gentle, humane remedies and his humane treatment of the mentally ill. His followers established temples called asclepions, temples of Asklepios, temples of healing. According to mythology, Asculapius had a number of children including Hygieia, the goddess of health (from whose name comes the word "hygiene") and Panaceia, the goddess of healing (from whose name comes por word "panacea" for a universal remedy). Today, the staff of Aesculapius is a commonly used symbol of medicine. It is the symbol of the American Medical Association (AMA) and many other medical societies.

+ sign
I could not find the meaning of the "plus" sign. I'm expecting it to be something very basic but cant find it. Do you know?