How do you know the market (I'm going to assume you are generally referring to the stock markets here) is "on the verge of a crash?" And what do you define as a "crash" - a decline of 10%? 20%? 40%? More?
At the end of the day, nobody knows what the markets will do in the short-term, and if anyone tells you they do, they are lying to you (and also lying to themselves). The markets have reached new all-time highs fairly recently, but that doesn't necessarily mean they are on the verge of crashing.
I'm not saying that there won't be a pullback (generally thought of as at least a 10% decline from a particular point) or even a full on bear market (generally thought of as at least a 20% decline from a particular point) in the near future. I have no idea. The only thing I can say with certainty is that in the future, there will be at least one more bear market - but I have no idea when it will be (and again, neither does anyone else, no matter what they might say).
If your concern is that the market will negatively react and/or "crash" when the Fed starts raising interest rates, there might be some negative impact, but a certain amount of that has already been priced into the markets, as the Fed has been doing everything in their power to telegraph their moves without explicitly stating when and what they will do, so as not to pidgeon hole itself into a certain course of action.
I do think that the first time they raise rates (likely sometime within the next 6-12 months), there will probably be a negative market reaction in the short-term, but as I said, I think that there is already the expectation of increasing rates factored into current prices (at least to a certain extent). In other words, if we expected rates to stay this low even longer than we already do, prices could conceivably be higher than they are at the moment.
So, my point here is don't assume that just because we are at, or near, all-time highs right now that we are automatically on the verge of a crash. And don't assume that just because the Fed will start raising rates in the relatively near future that it will cause the markets to come crashing down - it could, but it probably won't, though there is no way to know with any level of certainty since we have never had rates this low for this long, so we are in uncharted waters to a certain extent (notice I didn't say that there might not be a pullback or bear market, but I suspect that we probably won't see a "crash" - which I would generally tend to think of as something on the order of at least a 30 or 35%+ decline, though your personal definition of a "crash" might be completely different).
Now all of that being said, if you want to buy some silver bullion, that is fine. Precious metals certainly have their place in a well-diversified portfolio. However, when you are talking about bullion, you have to keep a few things in mind. (1) You have to find somewhere to store it. That might not be an issue if you are talking about a hundred 1 oz. bars or coins, or something like that, but if you are talking about larger bars, or larger amounts, then it can become an issue. (2) Bullion is not particularly liquid. You can always find someone who will buy it, but you may find it difficult to get the price you want for it. (3) If you have enough that would warrant seeking insurance or something like that, that is an added cost.
Ultimately, you can get exposure to the spot price of silver using an ETF (for example, SLV - note that this should not be considered a recommendation to purchase SLV, but merely used as an example) instead of purchasing actual bullion and it would be much easier to sell (effectively with the click of a mouse button) that selling physical bullion.
If you feel that when the market crashes we are going to enter a period where "survival of the fittest" comes into play and gold, silver, and canned foods will be the new currency, then SLV or any other ETF isn't going to do much good. So, in that case, bullion would be the better bet, despite its downsides, some of which are noted above.
At the end of the day, buying bullion is fine - it is simply an asset (so is a car, a luxury watch, a fancy handbag, your car, etc.). But I would not suggest buying silver buillion in anticipation of a "market crash" that may or may never come to fruition, and just like any other asset, I would not suggest having it make up too large a portion of your overall portfolio.
Hope that helps and good luck.
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