It's a hush seed nonce

bitcoin.cpp

@@ -10,7 +10,7 @@
 #include "serialize.h"
 #include "uint256.h"
 
-#define BITCOIN_SEED_NONCE  0x0539a019ca550825ULL
+#define HUSH_SEED_NONCE  0x0539a019ca550825ULL
 
 using namespace std;
 
@@ -79,7 +79,7 @@ class CNode {
   
   void PushVersion() {
     int64 nTime = time(NULL);
-    uint64 nLocalNonce = BITCOIN_SEED_NONCE;
+    uint64 nLocalNonce = HUSH_SEED_NONCE;
     int64 nLocalServices = 0;
     CAddress me(CService("0.0.0.0"));
     BeginMessage("version");

db.h

@@ -3,12 +3,10 @@
 // file LICENSE or https://www.gnu.org/licenses/gpl-3.0.en.html
 #include <stdint.h>
 #include <math.h>
-
 #include <set>
 #include <map>
 #include <vector>
 #include <deque>
-
 #include "coin.h"
 #include "netbase.h"
 #include "protocol.h"