It's very common to hear the term 'bull logo' when referencing specific varieties of silver engelhard ingots. To give a little more clarity to the term. The 'bull logo' does sort of resemble a bull with a circle and horns on the top. But that is not what this symbol represents.
^The logo to the left of the Engelhard hallmark. (Bull logo)
1st Series Canadian Ingot in 5 digit Serial Variation
Mintage <50
Recorded Sale: 3/11/2016 - $809.00 USD
Charles Engelhard was known as the platinum king. Simple enough the bull logo shown on the bar is the symbol for platinum!
This logo was only used on ingots that where manufactured with in the Canadian facilities. To touch on my first steem it post. I mentioned discussing the different varieties produced by Engelhard. These images are all Engelhard Canadian ingots. Hence the BULL!
^ 5th Series 10oz ingot in Canadian Varitation
Mintage <100
Recorded Sale: 2/20/2017 - $2450.00 USD
^ 16.075oz ingot Canadian Variation
Mintage <50
Recorded Sale: 6/22/16 - $1956.72 USD
There are many articles going into much further detail on www.allengelhard.com. They can be found under the suggested readings category. This website is a major resource with in the collectable silver community. Thank you for reading my post. Hope you enjoyed!