Yes, as a backup to a big phone number. It lets people text you in seconds, but it can never replace the number.
The quick answer
Yes, a QR code is a useful addition to a lost pet poster, as long as it is a backup and not a replacement for your phone number. A QR code lets someone send you a text or see a current update in a few seconds, which helps a person who would rather not make a phone call to a stranger. But most people seeing your poster from a car cannot scan it, some will not trust it, and it fails if printed too small or left in a wet sleeve. So keep the number big, and keep the code small and low on the page.
What a QR code is good for
The best use is a pre-filled text message. Someone scans it, their messages app opens with your number and a starter like I saw your lost dog at, and all they have to do is add the place. That removes the awkward part of calling a stranger, and it gives you the location in writing. A second good use is a link to a live page, such as a pinned post where the latest sighting is shown. That way, the poster stays useful even after the details change. Do not use a QR code for anything else, because more options means less action.
What it cannot do
A QR code cannot be read from a moving car or from across a road, and it asks a person to stop and take out a phone. People walking past a shop window or standing at a community board are the ones likely to scan it. So it helps most on flyers and in places where people stand still. It adds nothing to a poster that is meant for an intersection. Also, some people will not scan a code on a street notice at all, and with reason. Your poster needs to work completely for them without it.
Why some people will not scan
The Better Business Bureau has warned about fraudulent QR codes being used in a variety of scams. So if someone is careful about scanning, that is reasonable. You can help by labeling what the code does: Scan to text me a sighting. A code with a clear label is more likely to be used than a square of pixels with no explanation. Check your posters as you refresh them to make sure no one has added a sticker on top. If you see one, take it down, and tell your helpers.
How to make one that scans
Size matters most. Aim for about one inch square or a bit larger on paper, with a clear white border around it. Use dark squares on a light background, and do not invert the colors. Do not put a logo in the middle. Black and white printing is fine. Print it, then test it on two different phones, from about arm’s length, before you run a whole batch. Test it again in a sheet protector, since glare can block the camera. Our free tool can add a text-a-sighting code to your poster, already set up with your number.
Where it should go on the page
Put the code in the bottom corner, near the phone number, with its label beside it. It should not push the phone number down or make it smaller. If adding the code means shrinking the photo or the number, leave it off. The top priority on the page is still recognition, then the phone number. Think of the code as a small extra for the person standing close to it.
Privacy points
A QR code linked to a text message contains your number, just as the poster does, so it reveals nothing new. A code linked to a page may show more than you meant. If the page is your personal social media profile, a stranger can see your family photos and your address history. Make a separate public post or a dedicated page instead. Do not use a code that sends people to a form asking for their details, and be wary of any third-party service that wants a payment to host it.
Check that it still works
If your phone number or the page ever changes, every code printed needs replacing, so do not rely on a page that could expire. Some free QR makers switch off the link after a trial period or redirect through their own site. A code that directly contains the text or link does not depend on a third party. After your pet comes home, remove the posters and, if you linked to a post, update the post to say found so anyone scanning an old poster gets the right answer.
Sources
BBB Scam Alert on fraudulent QR codes: bbb.org/article/news-releases/27342-bbb-scam-alert-fraudulent-qr-codes-continue-to-be-used-in-a-variety-of-scams.