An assay card is what exactly?
Gold bars come with tamper-evident assay cards.  Usually, it provides the following vital data:

• The bar's weight, which is one ounce and 99.99% pure gold
• Seal or identifying mark of the refiner
• A one-of-a-kind serial number that matches the bar
• The signature or certification of the assayer

Gold bullion bars of a size ranging from small to medium, which are produced by renowned mints and refineries such as PAMP Suisse, Valcambi, and the Royal Canadian Mint, may occasionally carry assay cards as evidence of their authenticity.

Assay Cards Significance
An expert assayer uses an assay card to determine whether the gold bar in question is genuine. Gold bar verification gives you peace of mind and protects you from being defrauded or receiving counterfeit items.

• Bars sealed with their assay cards cost more.  Gold bars still in their original packaging are more dependable as they have not been altered in any manner.  Should you want to sell later, especially if gold prices are high, this may be important.
• Assay cards used to contain or safeguard gold bars.  The seal will be permanently destroyed if the bar is altered or removed in any manner.  This extra protection increases the strength of the bar and the collector's trust.
• Bars that are completely documented are preferred by private purchasers and dealers. On the secondary market, gold bullion bars for sale that have been assay-carded sell more quickly and for a higher price.
• Assay cards, which have unique serial numbers and mint-specific characteristics, help to simplify the process of confirming the origin of gold bars.  Many mints offer online serial number verification, hence boosting consumer confidence.