A "signatureless" transaction is a swiped or tapped Purchase for which a cardholder signature is not required because the Purchase amount is at or below the card's maximum Signatureless Dollar Value (SDV). Depending on the card type and how your terminal is configured, receipts may or may not print for a signatureless transaction.
To determine the maximum SDV for a card, print an EMV Parameters Report and locate the Contactless CVM Limit parameter under the report's section for the card. An SDV of 9999 means there is no maximum limit.