Radar reflectors are common on certain aircraft or even boats: https://www.gaelforcemarine.co.uk/en/GB/Trem-IOR-Radar-Reflector/m-3603.aspx?PartnerID=22&utm_so

Radar reflectors are common on certain aircraft or even boats: https://www.gaelforcemarine.co.uk/en/GB/Trem-IOR-Radar-Reflector/m-3603.aspx?PartnerID=22&utm_source=google&utm_medium=shopping&utm_campaign=UnitedKingdom&gclid=EAIaIQobChMIw8Sn6fvq3QIVCpPtCh3ArgWNEAQYASABEgKoefD_BwE https://www.gaelforcemarine.co.uk/en/GB/Trem-IOR-Radar-Refle... They used to equip some stealth aircraft during training with them so they could be more easily tracked.