what is digital signature certificate

{"cid":"91219627","title":"Visa Card Reader Handheld Pos Devices 60mm EMV Certificate With 2 PSAM Slot","imgUrl":"https:\/\/img.ismap.com\/nimg\/bd\/dd\/62f83cfef4d660d139de0898a729-200x200-1.jpg","attrs":{"Price":"US$25-35\/pc","Brand Name":"Tianyu","Model Number":"MP45","Minimum Order Quantity":"1pc","Delivery Time":"2-15days","Certification":"ISO ,Test Report,3C,RoHs","Place of Origin":"China","Payment Terms":"T\/T, Western Union, MoneyGram","Supply Ability":"20000-40000\/Month","Packaging Details":"Standard carton box","Brand name":"Tianyu","Power & Battery":"Battery lasts for more than 500 transactions by Magnetic Stripe Card or IC Card","Dimension":"111mm*60mm*12mm (approx.)","Programmable":"Support Secondary Development","Certificate":"PCI PTS, EMV L1 & L2","Power":"Battery lasts for more than 500 transactions by Magnetic Stripe Card or IC Card"}}

{"cid":"91190147","title":"High Speed RFID Smart Card With Full Color Offset Printing ISO9001:2008 Certificate","imgUrl":"https:\/\/img.ismap.com\/nimg\/e0\/77\/41698570ba0a6061a8caab8ebfb3-200x200-1.jpg","attrs":{"Price":"Negotiation","Brand Name":"ZDCARD","Model Number":"RFID Smart Card","Minimum Order Quantity":"500pcs","Delivery Time":"6-12 work days","Certification":"ISO 9001, 14001, OHSAS18001","Place of Origin":"Shenzhen, China","Payment Terms":"T\/T, Paypal, Western Union","Supply Ability":"100,000,000 pcs per month","Packaging Details":"2500PCS\/CTN","Finishes":"Glossy, Matte, Frost etc","Specification":"box: 22.2*9*5.4cm carton: 49*24.5*13cm","Frequency":"High Frequency","Material of Smart Card":"PVC, ABS, PET","Print":"Silkscreen, Full Color, UV for Smart Card","Certificate":"ISO9001:2008\/Ts, SGS"}}