Technically all designs and elements of designs belong to the designers until they grant permission of use. Or until they provide you with the necessary files. The conditions of use will vary from designer to designer. Some may requiring a link to a website, a contribution to their favorite charity... to some wanting monitory compensation. There is also information that you may need to know like if they own the images used in their designs, what the font names are and if there is any condition of use. Just because it is a concept or sample showing in the forum doesn't mean that it is FREE or isn't FREE or there aren't issues you need to be aware of. Contacting the designers is not only the smart thing to do it is also the polite thing to do. Remember always honor the ownership of logo designs of the designers and contact the designer by private message or email for the conditions of use.