I see this secretarial version on this pose pop up often enough on sites like eBay or ioffer to warrant a post.
Here's one which sold on eBay with the original mailing envelope for 100 bucks. A mailing label with an autograph from someone who isn't a confirmed mail signer is always a big red flag to me.
Another one with an $89.99 starting price:
This isn't the only secretarial autograph version, nor the only picture you'll find it on. The first thing I look at when deciding authenticity is the inscription if there is one because her cursive didn't change radically throughout her life. Here are a couple authentic examples of her signature: