Any string which was sign by secret key can be verify with public key. Some examples below

For sign a payload (nacl used from ton-crypto)

const signatureData = beginCell()
      .storeUint(123, 32)
      .storeCoins(toNano(123))
      .endCell()
nacl.sign(signatureData.hash(), YOUR_SECRET_KEY)

For check signature on another side (js) it can be like this:

  return nacl.sign.detached.verify(message, signature, pubkey)

OR if you want to check it in contract

			(int public_key) = load_data()
      slice ref = in_msg~load_ref().begin_parse();
      var signature = ref~load_bits(512);
      int is_valid = check_signature(slice_hash(in_msg), signature, public_key)

Some references

• wallet v4R2 with verify signature in external msg github
• TON Connect V2 and ton-proof verification on typescript and go github ts and github go