Council officers said they believed the thieves might try to sell the plaques to scrap metal merchants.
The authority said tighter rules meant that this was now more difficult, as anyone supplying scrap to a merchant must provide photo ID and a bank account, as payment in cash is illegal.
In addition, the plaques are made of gunmetal, which is worth considerably less than brass and other metals, according to the Local Democracy Reporting Service.
Councillor Richard Silvester, executive member for environment, said: “This kind of cruel theft beggars belief and I want to extend my sincere sympathy to anyone affected.
“The council will be working with the police to identify those responsible.
“I urge anyone who notices that the plaque for their loved one is missing to get in touch with the crematorium and we will help to get it replaced.”
