It's complicated and the implications and scope are not entirely clear.
The court stated that creative works such as web design qualify as a form of speech, and that the first amendment does not allow the government to use law to force creators to speak any message — especially one with which they disagree. Essentially, any business with something that might be considered speech as its product or service may be free to discriminate against protected classes. We aren't sure how far this will extend in practice, but I expect many will test it.
In this case of this post, it depends on what is being sold.
Edit: wrote this before my coffee and thus neglected to point out what replies said: political affiliation is not a protected class in America and these signs are a bit misleading. See replies.