Whatever you do; don't use Saran Wrap. I learned from experience and it wasn't pretty!

 Google is my friendly friend!

I have to say you win the prize for an original anonymous question.

If you cant buy something make something up. Heck duct tape if needed

I would just print one.

Candice A. Donofrio has my answer.  Mr. Google has many options. 

I just print up my own note and put it on the seat. 

I had water off at one of my listings recently and just put a sign on the front door...

I manage many REO homes and i use this DO NOT USE TAPE. That i put over each toilet.  For New Construction models I had also got these DO NOT USE CIRCLE STICKERS

What a bizarre question!  Believe it or not, we have a buyer who  is in contract to purchase a $1,300,000 home and the seller STILL will not allow their toilet to be used.  Our Broker had to take a "bush" stop outside their property as the issue after a 4 hour inspection got too desperate. Go figure the craziness of some people!

Amazon? Google? Definitely never had this question asked!

Vistaprint

GTS...

Amazon? Seems like you can get anything there.

Just Google it!

I have just printed up, in LARGE LETTERS, on a piece of colored paper, the message you have above, and taped it to the toilet lid.  I never had any issues of people using the facilities.  It's a quick fix!

The Google knows all.  Worst case, a note printed on bright paper and tape the lid shut.

Many good responses.

No idea, but maybe cleaning service couls answer that

GOOGLE

You have many great answers here.

I looked at the questions asked before and this one has a lot of great answers.

Have you tried making one yourself, not very difficult to do.

Really, you want to buy these in bulk?

You can use the wide ribbon from craft stores and tie a bow around the seat. I've seen stagers do this for builders.

Try a company call uline.com. If they don't have it, they will make it for you. https://www.uline.com/Product/ProductDetailRootItem?modelnumber=S-17342

Paper bands are not any more effective than a note on a sheet of paper.

If the property is vacant, seal the toilet with tape.

LOL If you put "Sanitized for your protection", on a toilet, a buyer will say how nice that they did this and use it anyway. If you ever want them, you can get 1000 for $19.95 here.

Use duct tape 

Google it, I say. Not a problem I've had to deal with on the whole.

Joe Pryor nailed this one!

Print a sheet with instructions. I’d then put a potted plant/ficusnext to the toilet, because they’ll need somewhere for relief. 

that's ridiculous.  

I have not had to buy these.

No idea.

Print a sign and tape up the seat

If the listing agent has presented themselves as a 'FULL SERVICE' agent, they will be present for ALL showings and can stand guard over the toilet lid. If they misrepresented themselves as full service and are not present to represent the seller, they should be FIRED.

A good wrap of a roll of plastic wrap from the kitchen cupboard does well also.

Need more such stuff, try ULine.

What is your contingency if someone really needs to use the bathroom...show them the backyard?

Already said here, Google it.

I doss not know.

I wish we knew.