There is no law or statute against simply writing on a cash bill. For instance,
it is not against the law to draw giant red lips on the queens portrait
( not quite sure why you would want to, but its not against the law).
However defacing currency with the intent to alter the bill to gain a benefit is
illegal. If someone alters a written instrument (such as a check) without
permission and with the intent to gain a benefit, then it is called forgery,
which is a crime. If one tried to alter a cash bill (like changing a $5 bill to
a $20 bill) for the purpose of presenting the altered bill to gain a benefit,
then that could be considered a forgery. Forgery of United States Currency in
this manner is called counterfeiting and carries with it very stiff penalties.
It is also illegal to deface currency if that defacement makes the currency unusable by obscuring it's value or serial numbers.
I encourage you to Google the question, and if anything has changed since I researched the matter, I will update this page.
If you will be
stamping your money, be sure to use "StazOn" ink. Its the only ink that will
stick to the new coated money.
StazOn
Ink is amazing! It lets you do that which most other inks do not – stamp on
non-porous surfaces without embossing. Try this ink on surfaces like glass,
metal, shrink plastic, cellophane, aluminum foil, leather, and acrylic – you'll
love it. The solvent-based ink is transparent in nature, resulting in a
beautiful "stained glass" look. StazOn is certain to become one of your favorite
inkpads, and it's acid-free!
Here is an example of a stamped bill:

Other Common Questions Include :
This site was officially launched on March 7 2010.
Sign up for an account to track your bills as they travel!
Enter the serial number, your current Canadian Postal Code, the value of the bill, and, if you want, a quick comment in the box such as bill condition, where you got it, etc.
You will then be presented with all the previous registered locations the bill was entered. It’s that simple! Have fun and see just how far your cash travels.
We do not sell any Follow Your Cash rubber stamps; but, if you want a stamp with Follow Your Cash on it, You can order this from any store that makes stamps.
Yes, we do. Your personal information is safe at Follow Your Cash as we will never sell or disclose your e-mail address or personal information to anyone.
Yes you can. Just go to this User Setting page and you can update all your user settings. DO NOT RE-REGISTER if you lost your e-mail address. Simply go to the LOG ON page to Forgot Password.
The only use of your e-mail address will be for verification, login purposes and to send an email when your bill receives a new hit (if turned on in your user settings). We will not use your e-mail for anything else. We have a strict policy here at follow your cash; your e-mail address will not be accessible to anyone other than our Management. We will also send optional hit notifications when your bill receives a hit.
If someone enters a new Postal Code that we don't have in the system, the distance and speed calculations are not valid and are disabled for that bill entry. The Postal Codes are occasionally updated to fix these issues.
The only other country we will use for tracking is the United States (coming soon).
There are three factors at work here.
First, if you choose to mark your bills, make sure your bills have the URL followyourcash.com clearly written on the bill. If people can't see your message, they are unlikely to visit the website and hit your bills.
Second, you'll need to spend your Follow Your Cash bills in locations likely to turnaround your bills to other people who will be more likely to be curious and come to the site. Convenience stores, arcades, fast food restaurants, malls and so on, seem to be good locations. If your bill(s) end up back at a bank, it could take months until the bill comes back into circulation.
The Third factor is pure luck. Some bills will be re-entered in hours or days, others will take up to four months or longer to show again.
Your FYC Score (follow your cash score) is your ranking on the site, the higher the score, the higher you move up on the ranking scale. Every time you enter a few bills, or receive a new hit, this number is adjusted. Anyone caught faking stats to move up the ranking scale will be immediately banned. Suspicions activity such as but not limited to, submitting sequential bills, several attempts to enter a bill in the system incorrectly etc, are auto sent to the admin for review. Average day users will not run into any issues with this, but someone trying to fake bills/hits would.