回答
沢山あります。どこで見かけたのか書いてくれると、正しい答えが分かります。SDG に限らず、acronym はどれでも、文脈の中でないと、何の意味なのか通じません。
SDG Sudanese Pound (currency)
SDG Sustainable Development Goal (various organizations)
SDG Soli Deo Gloria (Latin: To God Alone the Glory)
SDG Siding (railways)
SDG Sagittarius Dwarf Galaxy (astronomy)
SDG Software Development Governance
SDG Strategic Decisions Group
SDG School Development Grant (various organizations)
SDG Secoisolariciresinol Diglycoside (the main lignan in flaxseed)
SDG So Damn Good
SDG Steer Davies Gleave (UK consultancy firm)
SDG Spencer Davis Group (band)
SDG Short Duration Grazing
SDG Software Development Group (NCSA)
SDG Supplier Development Group (various locations)
SDG Sacred Dance Guild (Severna Park, MD)
SDG Stormont, Dundas & Glengarry (United Counties, ON)
SDG System Design Group
SDG System Dependence Graph
SDG Super Duper Games (various meanings)
SDG Sample Delivery Group
SDG Screen Directors Guild
SDG Super Dragon Gem (Conquer Online)
SDG Spiegel Design Group (Los Angeles, CA)
SDG Signed Directed Graph
SDG Saratoga Drama Group (California community theater)
SDG Superior Defender Gundam (anime)
SDG Steel Deck Girder (engineering)
SDG Sapporo Designer Gakuin (Sapporo, Japan)
SDG Subjective Difference Grade
SDG Single Digit Great
SDG Standby Diesel Generator (emergency bus power, nuclear power)
SDG Geometric Standard Deviation
SDG Single Digit Good (flash game FFR or Stepmania)
SDG Soil Density Gauge
SDG Slightly Decomposed Granite
SDG SAS Data Group
SDG Speed Defies Gravity Motors Inc. (Santa Ana, CA)
SDG Sindrome do Dedo Gordo (Brazil)
SDG Submarine Development Group
SDG Standard Design Guide
SDG Srpska Dobrovojacka Garda (Serbian Volunteer Guard)
SDG Supervisión Dirección General (Guatemala police supervision)
SDG Synthesis Design Group, Inc. (est. 2003)