Please note it will be compulsory to display this from 25th November 2019. The idea is that this allows clients to validate the firm. Here is a link to the article on the SRA website where you can read about this in more detail and obtain the SRA badge.
https://www.sra.org.uk/solicitors/resources/transparency/clickable-logo/
Here is a link to the company that supplies these for the SRA: https://www.yoshki.com/sra/