Not a lot to add to what William has said — yes, use Unicode and the Private Use Area.
You might, however, like to map some at least to Alpha Numeric characters for easier keyboard input, or perhaps you need some text characters that match the symbols? Something to consider.
Scan at the right resolution to get good import quality — aim for about 500 x 500 pixels.Size Does Matter
Cut and paste from an image editor like IrfanView can speed up input if you need to import a whole page of symbols, just scan the entire page. Scanning an Entire Alphabet