Also, how do you cash a cheque without validating signature (from whichever bank)?

Here in India atleast, cheques are cashed only at banks, and often are a/c payee only (no cash disbursed, only account transfer). They get truncated at the bank (basically scanned), and cleared overnight as a part of the CTS (a NPCI product).

However DDs (Demand Drafts) are your equivalent of cashiers cheques, and can be redeemed at par instantly, anywhere (or paid into an account).