Question

I’ve searched but I’m having trouble finding a conclusive conclusion. I would also be interested if this has any impact on SEO.

Answer 1

I would suggest not to use.

Reasons:

1. Google requests server with non encoded URL, even if link in the page is containing encoded (%27) version. This behavior may not be same for different browsers & other search engines. Also, Google displays non encoded version in the search results.

2. You can read link posted by Rahul Tripathi (http://productforums.google.com/forum/#!topic/webmasters/aKVMfwL6WgE) about the impact in search ranking with/without apostrophe.

If you still want to use apostrophe:

1. Ensure that your web server handles encoded & non encoded URL’s well.

2. Keep a track of your web-server logs for 404 errors due to improper usage of apostrophe by robots.

By the way currently we are running an experiment to record the behaviour of various search engines, while crawling pages with unsafe characters. You can find about it at http://app.searchenabler.com/experiments/.

One example test which we performed.
http://app.searchenabler.com/experiments/unsafe/%20!$&'()*+,-.:;%3C=%3E@[/]%5E_%60%7B%7C%7D~

(You can try to open above URL in different browser’s & check the behaviour)

Also you can see how google cached one such URL at
http://webcache.googleusercontent.com/search?q=cache:jkWRWOTPZXwJ:app.searchenabler.com/experiments/unsafe/%2520!%24%26‘()*%2B,-.:%3B%253C%3D%253E%40%5B%255C%5D%255E_%2560%257B%257C%257D~+&cd=1&hl=en&ct=clnk