public GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeType> signature(Key signature) {
        if (signature == null) {
            throw new NullPointerException("Signature must not be null");
        }
        this.signature = signature;
        return this;
    }
Sets some additional data to be mixed in to the memory and disk cache keys allowing the caller more control over
when cached data is invalidated.

<p>
    Note - The signature does not replace the cache key, it is purely additive.
</p>

@see com.bumptech.glide.signature.StringSignature

@param signature A unique non-null {@link Key} representing the current state of the
                 model that will be mixed in to the cache key.
@return This request builder.
core/src/main/java/com/bumptech/glide/GenericRequestBuilder.java