Make isValidSignature public

packages/contracts/src/contracts/current/protocol/Exchange/MixinSignatureValidator.sol

@@ -82,7 +82,7 @@ contract MixinSignatureValidator is
         address signer,
         bytes memory signature
     )
-        internal
+        public
         view
         returns (bool isValid)
     {

packages/contracts/src/contracts/current/protocol/Exchange/interfaces/ISignatureValidator.sol

@@ -39,4 +39,18 @@ contract ISignatureValidator {
         bool approval
     )
         external;
+
+    /// @dev Verifies that a signature is valid.
+    /// @param hash Message hash that is signed.
+    /// @param signer Address of signer.
+    /// @param signature Proof of signing.
+    /// @return Validity of order signature.
+    function isValidSignature(
+        bytes32 hash,
+        address signer,
+        bytes memory signature
+    )
+        public
+        view
+        returns (bool isValid);
 }

packages/contracts/src/contracts/current/protocol/Exchange/mixins/MSignatureValidator.sol

@@ -35,18 +35,4 @@ contract MSignatureValidator is
         PreSigned,  // 0x07
         Trezor      // 0x08
     }
-
-    /// @dev Verifies that a signature is valid.
-    /// @param hash Message hash that is signed.
-    /// @param signer Address of signer.
-    /// @param signature Proof of signing.
-    /// @return Validity of order signature.
-    function isValidSignature(
-        bytes32 hash,
-        address signer,
-        bytes memory signature
-    )
-        internal
-        view
-        returns (bool isValid);
 }