I have found that when we talk about ourselves we might say that we have some particular expertise in something and only rarely do we say "I am an expert". This is a personal branding mistake. For example, I might say that I have expertise in Java Software Architecture. But it would be better expressed as saying "I am a Java Software Architecture Expert". 

And another thing, the more you repeat this phrase - the more people will believe it and refer to you as the "Expert".  Saying that you have "expertise" is a commodity statement that is cast away from consciousness faster than you can finish the sentence.  When branding yourself - you must refer to yourself directly - and you must create real impressions in the minds of your audience.