How can I get a list with m tails? Python

So I need to create a list with m tails. The elements of the list will be a random choice between tail and head. I did like :

Def S(m):
    list=[]
    counter=0
    signs=["head","tail"]
    while counter<(m):
        list.append(random.choice(signs))
        for k in list:
            if k=="tail":
               counter+=1
    print(list)

So this one gives me a list but not with m tails. I think the while is wrong here but I am not sure how to write the code. Can you help me to change it?