Casey Research recently posted the above image with comments paraphrased below.
The previous ratio low point of the XAU gold stock index to the price of gold was .16, when gold traded around $270 an ounce in 2000. Today, the XAU is trading only 57% higher than in 2000, while the gold price has increased by 184%. As a rule of thumb, a ratio above the 25-year average indicates time to sell, and below its average time to buy. With the ratio bouncing off the lowest level since the inception of the XAU index, it signals a screaming buy for gold stocks.