Recently an industry guru who is compiling a study/book on transparency emailed me and asked "What are the practices that you think an agency should follow when it comes to transparency in writing content for a client's social media channels?"  This is what I emailed back:

I think if it is for the brand/company, then it is fine to just go ahead and post as the brand and not disclose exactly who the post is coming from. Just like a number of different employees might post on behalf of the company, you might also hire an agency to do so. And there is not that much difference between the agency and the employees, especially in today's world of contractors, part time workers, outsourcing, etc. People who see posts coming from a brand should understand that it is a person or a team of people posting on behalf of the company, and they need to consume the communication in that way. Just like you might get an advertisement or letter or email from a company and it is not "signed" by the marketing person or agency that created it, you might get a Tweet from a company but not know who exactly wrote it.

Now, in the case where you might be posting on behalf of a person, say the CEO of a brand/company, then I think complete transparency is called for. People deserve and expect to know if they are actually speaking with Marc Benioff or someone posting on his behalf, because there is a real person in the conversation. By the way, this does not mean that it is bad to have people post on your behalf. I think Guy Kawasaki on Twitter is a great example that being interesting is much more important than posting everything yourself.