.I'm glad that you found that info useful. However, I'm sad to see you state, “I just assumed everyone had one." In a nutshell, they most certainly don't! Have a look at <<http://freepages.work.rootsweb.com/~amateurheralds/research....
>> for some info on this subject and further at << http://www.sog.org.uk/leaflets/arms.html
>> - after reading those pieces of information, you can get back to us if you have any further queries. A coat of arms is Personal Property, not the property of the general public who think that they are entitled to use a particular armorial achievement, often because they have the same or similar surname.
When you say it's a "very old family" - if you just sit down and think about that statement and see that it applies to EVERY family in the world - we all came from ancestors. Tracing families back some 300 years is not 'old' at all as some people have traced (authentic documentation) back for well over a thousand years. The more important in society that the family was, the more documentation is available as a general rule, barring accidents like wars, etc. The maternal side of my family comes from a family name of Smith - there are millions of Smith (and spelling variations) families in the world and at least 500 of those were rightfully able to bear arms - but I can't go and use any of them and claim that they are my arms just because I am descended from a Smith family.
If there is anything further that we can help with, please ask away - we'll attempt to answer any queries that you may have