The Booster Club is exclusively for SFI Silver Builders and above. All Silver Builders automatically join when they reach this rank and are designated as Booster Club Qualified (BCQ). Every BCQ Affiliates gets 730 extra Daily Grand drawing entries annually and a 500-point prestige Booster Club badge (shown below).
In addition, BCQ Affiliates are designated with a special "membership ID card" icon (see image below) within the Genealogy, Affiliate Snapshots, and elsewhere around the Affiliate Center:
It identifies which of your affiliates are Booster Club members…on their Affiliate Snapshots and also at your Genealogy.