Actually, there were quite some discussions. The result: my girlfriend started anew and designed the following symbols for the subdivisions of Bitcoin.
That looks good, but I feel a bit uncomfortable when looking B and S logos have parallel lines through the symbol, that a little bit long, maybe better to make it short, and maybe on the S logo just go through of the line like the picture below:
It's just my suggestion, I am good if you think it's not like you want.
But, as far as I know, if we submit a proposal like a new symbol, must be approved by all community. If not, Maybe this will just be used as a reference if there is a change in the symbol in the future.