There are two ways to trade this spread.
1) Short gold/Long silver
2) Long silver (Do nothing with gold ) Silver has simply gone up more than gold in all points of the blue box - so it's up to you to determine the better strategy.
It seems to me that it might not be a good idea to short Gold, as the Gold/Silver ratio will likely not decrease as much as the ratio of many other things to Silver - for example Dollar/Silver, Real Estate/Silver, Retail/Silver, Small Caps/Silver, Tech/Silver etc.
I don't disagree. In reality, this ratio/spread tells us two important things. 1) Silver is a riskier asset/has more beta than gold. 2) Every time Gold/Silver reached this level since 1995 both gold and silver rallied significantly. The real value in this ratio is that it could be used as a supportive indicator that gold and silver may have bottomed - at least temporarily. Personally, I am not short this spread, but I certainly use it.