To remove currency symbol from Menu Block, you can use this CSS code.
#1. Menu Block on All Pages
span.currency-sign {
display: none;
}
#2. Specific Menu Block
First, find Menu Block ID.
In my example, it is: #block-yui_3_17_2_1_1738117986626_11930
Next, use CSS code.
#block-yui_3_17_2_1_1738117986626_11930 span.currency-sign {
display: none;
}