Add Account attachment to Chatter Post Automatically - salesforce

Question

I have need to add account attachments in Salesforce to the account chatter feed automatically. I've got the following code, which adds a chatter post for every object, not just account attachments, how can I make it specific to accounts? Or how can I make it specific to a certain file name?
trigger AttachFileToAccountFeed on Attachment (before insert) {
ID accountId;
list<FeedItem> listOfFeedFiles = new List<FeedItem>();
if(Trigger.isBefore){
for(Attachment attachment : trigger.new){
string checkIfAccount = string.valueof(attachment.description);
{
//Adding a Content post
accountId = attachment.ParentId;
FeedItem post = new FeedItem();
post.ParentId = accountId; //eg. Opportunity id, custom object id..
post.Body = 'Attachment added';
post.Type = 'ContentPost';
post.ContentData = attachment.body;
post.ContentFileName = attachment.Name;
post.Title = attachment.Name;
listOfFeedFiles.add(post);
}
}
}
if(listOfFeedFiles!=null){
insert listOfFeedFiles;
}
}

Answer 1

Here's what I ended up using:
trigger AttachFileToAccountFeed on Attachment (before insert) {
ID accountId;
list<FeedItem> listOfFeedFiles = new List<FeedItem>();
if(Trigger.isBefore){
for(Attachment attachment : trigger.new) {
// ensure the Id is an Account Id
if(attachment.ParentId.getSObjectType() != Account.SObjectType)
continue;
// ensure file contains Signed Authorization in File Name
if(attachment.Name.contains('Signed Authorization')) {
//Adding a Content post
accountId = attachment.ParentId;
FeedItem post = new FeedItem();
post.ParentId = accountId;
post.Body = 'Attachment added';
post.Type = 'ContentPost';
post.ContentData = attachment.body;
post.ContentFileName = attachment.Name;
post.Title = attachment.Name;
listOfFeedFiles.add(post);
}
}
}
if(listOfFeedFiles!=null){
insert listOfFeedFiles;
}
}