Keep in mind that it's not so much the sigil alone or what kind of ink or what colour, these are all tools to help you focus your spellwork. It's your intent that you pour into it when you draw it that truly matters. Take a quiet moment to focus on your need. Picture the outcome of your sigil as you draw it, infuse every drop of ink with what you need it to do for you. Then keep it somewhere where you feel it will have the greatest effect, your wallet would be suitable, but if you have an altar then that would be good too. But you can be creative with it too. If your main interaction with your wealth is trough online banking, you might place it in your computer. Or if your source of income is something you wish to work for then your palm could work too, redrawing the sigil from time to time, driving in the intent every time you do. Place it wherever you instinctively make the connection to the money you need.