It seems that the .woff files that are responsible for showing the icons do exist but they cannot be loaded on your server, for example: http://www.sissyraptopoulou.com/wp-content/themes/lay/assets/bootstrap/fonts/glyphicons-halflings-regular.woff
I see your textformats is using ttf files. But if I upload a .woff file, the server does not load the .woff file.
Please speak to your webhost, maybe there is an issue with your server configuration or htaccess configuration.