Symbol \stackrel{\smile}{\frown}: Meaning & LaTeX Command?

[LikeMath]

I just was wondering what is the meaning of this symbol
$\stackrel{\smile}{\frown}$.
It is used in the terminology of estimation of norms, I do not know if it is a standard notation, since I did not find anymore explanations. Also I do not know if there is a command to write it directly by LaTeX instead of "\stackrel{\smile}{\frown}".
Thanks in advance.

 

[LikeMath]

I just have found the symbol, so now the question is
what does it mean?
$\asymp$.