configure the sign plugin
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-gpg-plugin</artifactId>
<version>1.6</version>
+ <executions>
+ <execution>
+ <id>sign-artifacts</id>
+ <phase>verify</phase>
+ <goals>
+ <goal>sign</goal>
+ </goals>
+ </execution>
+ </executions>
</plugin>
</plugins>
</build>
