http://findbugs.sourceforge.net/: Annotation the FindBugs tool supports 
package javax.annotation.concurrent;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


ThreadSafe
The class to which this annotation is applied is thread-safe. This means that
no sequences of accesses (reads and writes to public fields, calls to public
methods) may put the object into an invalid state, regardless of the
interleaving of those actions by the runtime, and without requiring any
additional synchronization or coordination on the part of the caller.

/**
 * ThreadSafe
 * 
 * The class to which this annotation is applied is thread-safe. This means that
 * no sequences of accesses (reads and writes to public fields, calls to public
 * methods) may put the object into an invalid state, regardless of the
 * interleaving of those actions by the runtime, and without requiring any
 * additional synchronization or coordination on the part of the caller.
 */
@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.CLASS)
public @interface ThreadSafe {
}