Correct mathematical symbol to represent "subtype"

If this question doesn't make sense, it's probably because I might be confused with the term subtype.

What is the correct mathematical symbol for subtype ?
if B is a subtype of A, which do I write:

1. B â‰¤ A
2. B <: A

Thanks.

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Mostly <:

I think <: is most common, but you'll probably see some variation. It also depends a bit on the context. Sometimes one might want to consider the subtype relation as just another partial order, in which case it might be desirable to use another symbol.

Proper or improper subtype?

I've also seen the subset operator (⊂ for the proper case, ⊆ for when equality is included) used.

â‰¤ and âŠ‚ are already defined

I would think that <: would be the best representation since the above mentioned ones are already defined to have other meanings in mathematics. I haven't seen <: and :> used in any context (other than pointy mouthed smileys :) that it would make the most sense and create the least confusion over the other suggestions.