Filter the blog title displayed in the header

Remove that filter/function and apply your markup in the PHP template/page file. If you need help post where you output the title.

---

CLASS

Here is how I might set this up using a class:

if ( ! class_exists( 'ThemeCustomizations' ) ) {
    class ThemeCustomizations {
        static $inBody = false;

        public static function set_in_body_true() {
            static::$inBody = true;
        }

        public static function set_in_body_false() {
            static::$inBody = false;
        }

        public static function filter_bloginfo( $name, $show = null ) {
            if ( 'name' == $show && static::$inBody ) {
                $name = "<span class="info-style">Info</span>" . "<span class="psi-style">Psi</span>" . "<span class="md-style">.md</span>";
                return "$name";
            } else {
                return $name;
            }
        }
    }
}

add_action( 'wp_head',   array ( 'ThemeCustomizations', 'set_in_body_true' ), PHP_INT_MAX );
add_action( 'wp_footer', array ( 'ThemeCustomizations', 'set_in_body_false' ), 0 );
add_action( 'bloginfo',  array ( 'ThemeCustomizations', 'filter_bloginfo' ), 10, 2 );

STATIC

And using a function’s statically scoped variable:

function prefix__is_in_body( $isTrue = null ) {

    // static initializer is false
    static $inBody = false;

    // only overwrite if boolean supplied
    if ( is_bool( $isTrue ) ) {
        $inBody = $isTrue;
    } 

    // return regardless of getter/setter
    return $inBody;
}

add_action( 'wp_head',   function(){ prefix__is_in_body(true); }, PHP_INT_MAX );
add_action( 'wp_footer', function(){ prefix__is_in_body(false); }, 0 );
add_action( 'bloginfo',  function($name, $show = null){
    if ( 'name' == $show && prefix__is_in_body() ) {
        $name = "<span class="info-style">Info</span>" . "<span class="psi-style">Psi</span>" . "<span class="md-style">.md</span>";
        return "$name";
    } else {
        return $name;
    }
}, 10, 2 );

---

MAGIC

Singleton & Factory patterns + PHP magic methods.

if ( ! class_exists( 'Magic' ) ) {
    class Magic {
        private static $__ = array ();
        public         $_  = array ();

        function __construct( $args = null ) {
            if ( is_array( $args ) ) {
                foreach ( $args as $k => $v ) {
                    $this->{$k} = $v;
                }
            }
            return $this;
        }

        public static function instance( $id = '', $args = null ) {
            if ( ! isset( self::$__[ $id ] ) ) {
                self::$__[ $id ] = new Magic($args);
            }
            return self::$__[ $id ];
        }

        public function __get( $k ) {
            return isset( $this->_[ $k ] ) ? $this->_[ $k ] : null;
        }

        public function __set( $k, $v ) {
            return $this->_[ $k ] = $v;
        }

        public function __call( $k, $a ) {
            if ( isset($this->_[ $k ]) && is_callable( $this->_[ $k ] ) ) {
                return call_user_func_array( $this->_[ $k ], $a );
            }
        }
    }
}

Now with the Magic class you can do this;

$m = Magic::instance( '', array (
    'isBody'             => false,
    'action_wp_head'     => function() { Magic::instance()->isBody = true;  },
    'action_wp_footer'   => function() { Magic::instance()->isBody = false; },
    'filter_wp_bloginfo' => function( $output, $show ) {
        return ( 'name' == $show && Magic::instance()->isBody ) ? '<span class="info-style">Info</span><span class="psi-style">Psi</span><span class="md-style">.md</span>' : $output;
    },
));

add_action( 'wp_head',   array ( $m, 'action_wp_head' ), PHP_INT_MAX );
add_action( 'wp_footer', array ( $m, 'action_wp_footer' ), 0 );
add_filter( 'bloginfo',  array ( $m, 'filter_wp_bloginfo' ), 10, 2 );