Google added a new business attribute for small businesses to showcase they are small. You can add it under your Google Business Profile, where you edit your listing and select your attributes.

Go to your Business Profile by searching for my business
To edit your business info: With Google Search, select Edit profile. or with Google Maps, select Edit profile and then > Business information.
Near the top, select the More tab.
Select the category you want to change.
Next to the attribute, select Yes or No.
When you’re finished updating your attributes, select Save.

Here is a screenshot:

Then eventually, it should show up in your Business profile in Google Search and Google Maps:

This is how it looks like when you are also in Merchant Center, your products also get the label:

Google announced this on its blog saying, “Starting today, merchants can identify themselves with a new small business attribute on Search and Google Maps. Products in Search sold by businesses with that attribute will have a “small business” label on them, as will businesses on Maps. These new labels will make it easier for shoppers to narrow down their searches and be intentional about shopping with their favorite (or soon-to-be-favorite) businesses.”

Here is the email Google sent small businesses about this new attribute:

It says:

Forum discussion at X.

Update: You can even filter by this attribute for some queries: